Ok, I managed to show icons with this css code:
.posted-on:before {
content: "\f073";
font-family: FontAwesome;
font-weight: normal;
font-style: normal;
display: inline-block;
text-decoration: inherit;
position: relative;
margin-right: 5px;
width: 13px;
text-align: center;
}
.byline:before {
content: "\f007";
font-family: FontAwesome;
font-weight: normal;
font-style: normal;
display: inline-block;
text-decoration: inherit;
position: relative;
margin-right: 5px;
width: 13px;
text-align: center;
}