Follow this link;
http://www.soberrecovery.com/forums/...=editsignature
Here are your two options;
If you have an image on your harddrive, use the 2nd option and click browse to locate the image. Select the image and click open. (It might be slightly different if you're using a Mac) Then click on preview to look at it first, or click on save signature.
Either upload an image to imageshack like Vic says, or use tinypic.com
If you still have trouble, send me a PM with the link you already have, and I'll help.