diff --git a/src/app.module.ts b/src/app.module.ts
index e762e5f825..bb0dad5ba0 100644
--- a/src/app.module.ts
+++ b/src/app.module.ts
@@ -4,6 +4,7 @@ import { TypeOrmModule } from '@nestjs/typeorm';
 import { AppController } from './app.controller';
 import { GetConfig } from './config/config';
 import { IntegrationModule } from './integration/integration.module';
+import { SignatureVisibilityInterceptor } from './shared/auth/signature-visibility.interceptor';
 import { TfaEnforcementInterceptor } from './shared/auth/tfa-enforcement.interceptor';
 import { SharedModule } from './shared/shared.module';
 import { SubdomainsModule } from './subdomains/subdomains.module';
@@ -11,9 +12,13 @@ import { SubdomainsModule } from './subdomains/subdomains.module';
 @Module({
   imports: [TypeOrmModule.forRoot(GetConfig().database), SharedModule, IntegrationModule, SubdomainsModule],
   controllers: [AppController],
-  // Global backstop enforcing STRICT app-2FA on every route for a mail-origin staff session (tfaRequired).
-  // Only needs ModuleRef + Reflector (both globally available), so no extra module imports are required.
-  providers: [{ provide: APP_INTERCEPTOR, useClass: TfaEnforcementInterceptor }],
+  providers: [
+    // Global backstop enforcing STRICT app-2FA on every route for a mail-origin staff session (tfaRequired).
+    // Only needs ModuleRef + Reflector (both globally available), so no extra module imports are required.
+    { provide: APP_INTERCEPTOR, useClass: TfaEnforcementInterceptor },
+    // Strips User.signature from every HTTP response whose caller is not ADMIN (or SUPER_ADMIN).
+    { provide: APP_INTERCEPTOR, useClass: SignatureVisibilityInterceptor },
+  ],
   exports: [],
 })
 export class AppModule {}
diff --git a/src/shared/auth/__tests__/signature-visibility.interceptor.spec.ts b/src/shared/auth/__tests__/signature-visibility.interceptor.spec.ts
new file mode 100644
index 0000000000..edb09ae9e4
--- /dev/null
+++ b/src/shared/auth/__tests__/signature-visibility.interceptor.spec.ts
@@ -0,0 +1,123 @@
+import { createMock } from '@golevelup/ts-jest';
+import { CallHandler, ExecutionContext } from '@nestjs/common';
+import { MODULE_METADATA } from '@nestjs/common/constants';
+import { APP_INTERCEPTOR } from '@nestjs/core';
+import { firstValueFrom, Observable, of } from 'rxjs';
+import { UserRole } from 'src/shared/auth/user-role.enum';
+import { User } from 'src/subdomains/generic/user/models/user/user.entity';
+import { SignatureVisibilityInterceptor } from '../signature-visibility.interceptor';
+
+// Self-referencing shape for the cycle case - the interceptor must terminate on it.
+interface Cyclic {
+  ref?: Cyclic;
+}
+
+describe('SignatureVisibilityInterceptor', () => {
+  let interceptor: SignatureVisibilityInterceptor;
+  let next: CallHandler;
+  let handle: jest.Mock;
+
+  const context = (request: unknown): ExecutionContext =>
+    createMock<ExecutionContext>({ switchToHttp: () => ({ getRequest: () => request }) as never });
+
+  // The interceptor is typed against `unknown` payloads, so each case states the shape it put in.
+  const run = async <T>(request: unknown): Promise<T> =>
+    firstValueFrom((await interceptor.intercept(context(request), next)) as Observable<T>);
+
+  beforeEach(() => {
+    handle = jest.fn();
+    next = { handle } as CallHandler;
+    interceptor = new SignatureVisibilityInterceptor();
+  });
+
+  it('passes a User entity through unchanged when the caller role is ADMIN (fast path)', async () => {
+    const user = Object.assign(new User(), { id: 1, signature: 'secret-sig', address: 'addr-1' });
+    handle.mockReturnValue(of(user));
+
+    const result = await run<User>({ user: { role: UserRole.ADMIN } });
+
+    expect(handle).toHaveBeenCalled();
+    expect(result).toBe(user);
+    expect(result.signature).toBe('secret-sig');
+  });
+
+  it('passes a User entity through unchanged when the caller role is SUPER_ADMIN', async () => {
+    const user = Object.assign(new User(), { id: 2, signature: 'secret-sig', address: 'addr-2' });
+    handle.mockReturnValue(of(user));
+
+    const result = await run<User>({ user: { role: UserRole.SUPER_ADMIN } });
+
+    expect(handle).toHaveBeenCalled();
+    expect(result).toBe(user);
+    expect(result.signature).toBe('secret-sig');
+  });
+
+  it('strips signature from a User entity when the caller role is SUPPORT, keeping other properties', async () => {
+    const user = Object.assign(new User(), { id: 3, signature: 'secret-sig', address: 'addr-3' });
+    handle.mockReturnValue(of(user));
+
+    const result = await run<User>({ user: { role: UserRole.SUPPORT } });
+
+    expect(result.signature).toBeUndefined();
+    expect(result.address).toBe('addr-3');
+  });
+
+  it('strips signature from a User entity when there is no request.user (unauthenticated)', async () => {
+    const user = Object.assign(new User(), { id: 4, signature: 'secret-sig', address: 'addr-4' });
+    handle.mockReturnValue(of(user));
+
+    const result = await run<User>({});
+
+    expect(result.signature).toBeUndefined();
+    expect(result.address).toBe('addr-4');
+  });
+
+  it('recursively strips signature from nested User entities (userData.users[])', async () => {
+    const userA = Object.assign(new User(), { id: 10, signature: 'sig-a' });
+    const userB = Object.assign(new User(), { id: 11, signature: 'sig-b' });
+    const payload = { userData: { users: [userA, userB] } };
+    handle.mockReturnValue(of(payload));
+
+    const result = await run<{ userData: { users: User[] } }>({ user: { role: UserRole.SUPPORT } });
+
+    expect(result.userData.users[0].signature).toBeUndefined();
+    expect(result.userData.users[1].signature).toBeUndefined();
+  });
+
+  it('leaves a non-User object with its own signature property untouched (must not filter by field name)', async () => {
+    // Critical case: other entities (e.g. RealUnit registrations) also carry a `signature` field and
+    // must not be stripped — only `instanceof User` may trigger removal.
+    const other = { id: 1, signature: 'not-a-login-credential' };
+    handle.mockReturnValue(of(other));
+
+    const result = await run<{ signature: string }>({ user: { role: UserRole.SUPPORT } });
+
+    expect(result.signature).toBe('not-a-login-credential');
+  });
+
+  it('does not loop infinitely on a cyclic object graph', async () => {
+    const a: Cyclic = {};
+    const b: Cyclic = { ref: a };
+    a.ref = b;
+    handle.mockReturnValue(of(a));
+
+    const result = await run<Cyclic>({ user: { role: UserRole.SUPPORT } });
+
+    expect(result).toBe(a);
+    expect(result.ref).toBe(b);
+  });
+
+  // The cases above exercise the interceptor directly, so none of them would notice if the global
+  // registration were dropped - the protection would be silently gone. This pins the wiring itself.
+  it('is registered globally as an APP_INTERCEPTOR', async () => {
+    const { AppModule } = await import('src/app.module');
+    const providers = Reflect.getMetadata(MODULE_METADATA.PROVIDERS, AppModule) as {
+      provide?: unknown;
+      useClass?: unknown;
+    }[];
+
+    expect(providers.some((p) => p.provide === APP_INTERCEPTOR && p.useClass === SignatureVisibilityInterceptor)).toBe(
+      true,
+    );
+  });
+});
diff --git a/src/shared/auth/signature-visibility.interceptor.ts b/src/shared/auth/signature-visibility.interceptor.ts
new file mode 100644
index 0000000000..e74a1a8be1
--- /dev/null
+++ b/src/shared/auth/signature-visibility.interceptor.ts
@@ -0,0 +1,58 @@
+import { CallHandler, ExecutionContext, Injectable, NestInterceptor } from '@nestjs/common';
+import { Observable } from 'rxjs';
+import { map } from 'rxjs/operators';
+import { hasRoleAccess } from 'src/shared/auth/role.guard';
+import { UserRole } from 'src/shared/auth/user-role.enum';
+import { User } from 'src/subdomains/generic/user/models/user/user.entity';
+
+// Global strip of the login credential on `User.signature` for non-admin HTTP responses.
+//
+// At least 13 endpoints surface this column today through relations; `Transaction.user` is eager and
+// carries it even when no user relation was requested. Filtering per endpoint would be incomplete and
+// would be forgotten on every new admin read path — this interceptor closes the leak in ONE place.
+//
+// Filtering is by entity type (`instanceof User`), never by property name: other entities in the repo
+// also carry a field named `signature` (e.g. RealUnit registrations) and must not be stripped.
+// Missing `request.user` is treated as non-admin (fail-closed), not as a special pass-through.
+// A WeakSet tracks visited objects so cyclic entity graphs (bidirectional relations) do not loop.
+//
+// Registered as an APP_INTERCEPTOR next to TfaEnforcementInterceptor.
+@Injectable()
+export class SignatureVisibilityInterceptor implements NestInterceptor {
+  intercept(context: ExecutionContext, next: CallHandler): Observable<unknown> {
+    const request = context.switchToHttp().getRequest();
+    const role: UserRole | undefined = request.user?.role;
+
+    // FAST PATH: ADMIN / SUPER_ADMIN traffic keeps the full response; no map, no walk.
+    // This is the bulk of admin-endpoint traffic and must stay a single role check.
+    if (hasRoleAccess(UserRole.ADMIN, role)) return next.handle();
+
+    return next.handle().pipe(map((data) => this.stripSignatures(data)));
+  }
+
+  private stripSignatures(value: unknown, seen: WeakSet<object> = new WeakSet()): unknown {
+    if (typeof value !== 'object' || value === null) return value;
+    if (value instanceof Date) return value;
+    if (value instanceof Buffer) return value;
+    if (seen.has(value as object)) return value;
+
+    seen.add(value as object);
+
+    if (Array.isArray(value)) {
+      for (const element of value) {
+        this.stripSignatures(element, seen);
+      }
+      return value;
+    }
+
+    if (value instanceof User) {
+      delete (value as { signature?: string }).signature;
+    }
+
+    for (const key of Object.keys(value as object)) {
+      this.stripSignatures((value as Record<string, unknown>)[key], seen);
+    }
+
+    return value;
+  }
+}
diff --git a/src/subdomains/generic/user/models/user/user.entity.ts b/src/subdomains/generic/user/models/user/user.entity.ts
index 0699ce0e24..269e0d3580 100644
--- a/src/subdomains/generic/user/models/user/user.entity.ts
+++ b/src/subdomains/generic/user/models/user/user.entity.ts
@@ -28,6 +28,10 @@ export class User extends IEntity {
   @Column({ length: 256, nullable: true })
   addressType?: UserAddressType;
 
+  // Login credential: for DeFiChain and custodial Lightning the stored value IS the secret that
+  // authenticates a sign-in (see AuthService.verifySignature). Loaded normally like any other column;
+  // `SignatureVisibilityInterceptor` (registered as a global APP_INTERCEPTOR) strips it from every HTTP
+  // response whose caller does not satisfy the ADMIN role requirement.
   @Column({ type: 'text', nullable: true })
   signature?: string;