There seems to be a little problem recently with people's signatures being a bit too big... It's not a major problem, but they are required to be within a certain size limit, otherwise the sigs take over people's posts and it means it unnecessarily increases the size of the whole page.
Wherever possible, admin will try to re-size an image if it is too big, however the signature may be removed without warning if it's too big...
The maximum size a signature should be is 470 pixels wide and 150 pixels high, and the image shows the MAXIMUM size a signature should be.
You could have more than one image in your signature, however all images in it must NOT cover a greater area than that shown in the white image above. Similarly, if you place text under an image, this should be taken into account and the image made smaller if you plan to place text underneath...