Custom signatures
It's possible to customise your signature, and you can put 'code' in it to have different colours, etc. Pictures aren't allowed; hence, mine isn't an icon, it's just text characters with different colours.
You put the code in your preferences signature box, and checkmark the 'user raw signatures'; please note that it's fiddly, and easy to get it wrong, so it's best to test signing in a user sandbox area.
When using 'raw signatures' in your preferences, you need to manually include the links to your user and talk pages.
An example code is;
<small><span style="border:1px solid #0000ff;padding:1px;">[[User:Chzz|<b>Chzz</b>]] : [[User_talk:Chzz|<font style="color:#accC10;background:#0000fa;"> Chat </font>]] </span></small>
Note that you should always include your name (or part of it), a link to your user page and talk page.
Perhaps the easiest way to learn more is simply to look at other peoples signatures, by editing the page they've signed on, and looking at the code. There are some here. For an example page with several, ahem, interesting signatures, see the April 1st Request for signatureship.
Make sure things are OK before signing on any talk pages (particularly that the links to your own pages work). If it all goes horribly wrong, see Wikipedia:How to fix your signature.
For much more info on this, see Wikipedia:SIGNATURE#Customizing_your_signature.
If you need any help with it, ask here or talk to us live.