export class AuthService {) { }
  logout() {
   Alert('User is logging off..');
  }
}

<ion-header>
  <ion-navbar>
    <button ion-button menuToggle>
      <ion-icon name="menu"></ion-icon>
    </button>
    <ion-title>
      <img class="header-logo pull-left" src="assets/img/logo.jpg" alt="">
      <ion-icon name="log-out" class="pull-right logout-action" (click)="logout()"></ion-icon>
    </ion-title>
  </ion-navbar>
</ion-header>