copied straight from my profile: (Max 400 characters including tags)
Sig Images, brief instructions: Go to a free image host (like: http://www.tinypic.com), upload your image there. Paste in the box above the URL they give you to link to the image. Highlight it in the box above then click the image button above. Alternatively, if your image host give you a link with [IMG][/IMG] use that link and it will be ready as soon as you paste it into the box above.
You are only allowed one image in your sig, and must be no bigger than 500 pixels wide and 200 pixels tall, otherwise you could get your sig removed and locked.
For more extensive instructions, please read this thread: Avatar and Sig Image Tutorial.
Always forgive your enemies - Nothing annoys them so much