If you want data validation too
<!-- form -->
<form name="loginForm">
...
<input type="email" ng-keyup="$loginForm.$valid && $event.keyCode == 13 && signIn()" ng-model="email"... />
<input type="password" ng-keyup="$loginForm.$valid && $event.keyCode == 13 && signIn()" ng-model="password"... />
</form>
The important addition here is $loginForm.$valid
which will validate the form before executing function. You will have to add other attributes for validation which is beyond the scope of this question.
Good Luck.