The image alone is 100px high, so that's already the max limit. Depending on your browser, you may be able to see it if you right click and go to properties, or you can try just saving it to your desktop and looking at the file properties there.
Yeah, in general you can just PM me or a global mod, or report one of the user's posts and we'll see it that way.
Your sig is 80px high, so there's plenty of room for a line of text. The avatar is fine also.
Everyone should be able to have a signature, no matter what the post count.