Assuming this is what the HTML looks like
<div class="form-group required">
<label class="col-md-2 control-label">E-mail</label>
<div class="col-md-4"><input class="form-control" id="id_email" name="email" placeholder="E-mail" required="required" title="" type="email" /></div>
</div>
To display an asterisk on the right of the label:
.form-group.required .control-label:after {
color: #d00;
content: "*";
position: absolute;
margin-left: 8px;
top:7px;
}
Or to the left of the label:
.form-group.required .control-label:before{
color: red;
content: "*";
position: absolute;
margin-left: -15px;
}
To make a nice big red asterisks you can add these lines:
font-family: 'Glyphicons Halflings';
font-weight: normal;
font-size: 14px;
Or if you are using Font Awesome add these lines (and change the content line):
font-family: 'FontAwesome';
font-weight: normal;
font-size: 14px;
content: "\f069";