This can be done with no additional mark-up, just a new class (which you would use anyway) and a pseudo element.
JSFiddle Demo
HTML
<i class="fa fa-envelope fa-5x fa-border icon-grey badge"></i>
CSS
*.icon-blue {color: #0088cc}
*.icon-grey {color: grey}
i {
width:100px;
text-align:center;
vertical-align:middle;
position: relative;
}
.badge:after{
content:"100";
position: absolute;
background: rgba(0,0,255,1);
height:2rem;
top:1rem;
right:1.5rem;
width:2rem;
text-align: center;
line-height: 2rem;;
font-size: 1rem;
border-radius: 50%;
color:white;
border:1px solid blue;
}
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