FYI: Make sure that you check out the
Community Guidelines when it comes to the size of your signature, too.
QUOTE
SIGNATURES
Signatures should not take up more than 300 pixels of vertical space (equivalent to 20 lines of text) and 590 pixels of horizontal space (to prevent from stretching). Signature images should be less than 100kB in file size when combined. They may only contain references and links to personal pages, such as your blogs and profiles; references and links to anything that is not personal, such as websites and outside forums are not allowed.