Back in 2005 as a proof of concept a friend of mine decided to prove to the board moderators a particular anime forum he was part of how bad having no limitations on signatures could be.
They basically had a "whatever you want!" policy on sigs, which was kind of rediculous. Most posts on that board were about 30% post, 70% signature.
To show them the error of their ways my friend created a signature with several-thousand-by-several-thousand pixel multi-layered javascript fade-in divs covered in nothing but rows of smileys that faded in and moved horizontally around the page while using the marquee tag.
Suffice to say after both the forum's web server and many senior posters' PCs had metaphores involving unpleasant reproductive acts applied to them, the policy was reversed. My friend thrived in our collective mirth.
Moral of the story? Big signatures = bad
