http://forum.lowyat.net/index.php?act=faq&article=7

There is a whole article there on the rules and regulations with regards to signatures. Break it and you get a warning.

Signature images are hosted elsewhere, so we can't limit it automatically since it doesn't get uploaded to our server.

animated gif's are allowed, as long as its below the size restrictions. Size here is not the width x height but how many kB's the file uses. There are still dial up users who visit the forum and extremely large animated gifs take a very long time to download.