The Post with Icons widget and other theme functions may display an icon based on the current post format. You can easily filter the format icon classname using a filter like in the example above. You can refer to the Theme Icons list for the correct classname or use your own classname to target via CSS or a 3rd party icon set.
add_filter( 'wpex_post_format_icon', function() {
$format = get_post_format();
switch ( $format ) {
case 'video':
$icon = 'ticon ticon-video-camera';
break;
case 'audio':
$icon = 'ticon ticon-music';
break;
case 'gallery':
$icon = 'ticon ticon-file-photo-o';
break;
case 'quote':
$icon = 'ticon ticon-quote-left';
break;
default:
$icon = 'ticon ticon-file-text-o';
break;
}
return $icon;
} );