<style>
.asterik-span{
    color: red; font-family: bold; font-size: 16px;
 }
.select-diag{
   width:90%;border:1px solid #ddd; border-radius:3px;height:32px;
 }
</style>

<select  class="select-diag">
    <option >Value1</option>
    <option >Value2</option>
    <option >Value3</option>
</select>
<span class='pull-right asterik-span'>*</span>