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Click User Control Panel, then Profile, then Edit Signature, you can then type in a signature, upload a pic from your computer or insert a hosted pic.

i hope this helps too.

1- go to the User Control Panel.
2- click on Profile.
3- click on Edit Signature.
4- Click on Image (if you want to add a picture to your signature, i uploaded mine to tinypic.com and got it from there), here you can type the contents of your signature.
5-place the url of your hosted picture between the [img] icons.