Well... it's a fair idea, but stopping images over a certain size is tricky unless we control all the images. Which, of course, we don't. If we had control of all the images (i.e. you had to upload them to us first before using them in a sig), we could easily maintain a database of image sizes and restrict accordingly.

However, as it is now (i.e. you make links to external images), we'd need to load each image from that server every time the signature is called, get the image dimensions (if it's even a valid image file to begin with), and work from there. That'd make a horrendous strain on the server (having to contact X number of other servers per page, where X is the number of unique external image links on the page) and would stall out a lot of pageloads if a server stopped responding and the JCF had to wait for it to timeout before going on.

So, that's not quite gonna work, is what I'm saying. :-)