Quando coloquei "Voltar" dentro da tag o botão sumiu no ios e android e ficou com fundo brando.
<ion-side-menu-content>
<ion-nav-bar class="bar bar-positive">
<ion-nav-back-button>Voltar</ion-nav-back-button>
<ion-nav-buttons side="left" >
<button class="button button-icon button-clear ion-navicon" menu-toggle="center"></button>
</ion-nav-buttons>
</ion-nav-bar>
<ion-nav-view name="menuContent"></ion-nav-view>
</ion-side-menu-content>