I can't speak for Firefox or IE, but if you right click in Chrome (and probably other browsers) over the signature area and click "Inspect Element" or something along those whereabouts, you'll see the signature become highlighted with dimensions. It works for images only, and sometimes text, but not always. Also, if you see a signature with no CSS and a scrollbar, just assume it's too tall :P
Also, why the name change back? o_O