if you want use html you can change postbit_online/postbit_offline templates
else if you want use css , you can add any class or ID to your offline and online elements and use icon for that element like this
.YOURCLASS{
position:relative;
}
. YOURCLASS:before {
content: "\25AE"; /* this is your text. You can also use UTF-8 character codes as I do here */
font-family: FontAwesome;
}
in content property you can put your icon as content code that you can find in fontawsome and change your font-family name based on your fontawsome version font-family name