uso para expresar campo requerido al usuario

agreements.html

<div class="form-group required">
    <label class="col-md-2">&#160;</label> <!-- remove class control-label -->
    <div class="col-md-4">
        <div class="checkbox">
            <label class='control-label'> <!-- use this class as the red * will be after control-label -->
                <input class="" id="id_tos" name="tos" required="required" type="checkbox" /> I have read and agree to the Terms of Service
            </label>
        </div>
    </div>
</div>

requirement-control.css

.form-group.required .control-label:after {
  content:"*";
  color:red;
}