Userbars were quite popular before signature pictures defeated them.
Basically, a userbar is a small image designed to be put into a forum user's signature to designate his likes, dislikes and membership.
Some examples are:
A userbar I made for an on-line browser RPG in which I was an admin member. I still am an admin there, but I don't do much things there nowadays. 350*19 or 350*20 px.
A userb... I mean, bigbar for the game "The Ur-Quan Masters", which is Star Control II open-sourced. 350*40 px.
As you can see, in both cases I used a few images from the game, and drew the rest using Fireworks vector tools and my lame mouse-drawing skills.
For some reason, there is no English Wikipedia entry on them. =) If you know any other language:
http://ru.wikipedia.org/wiki/%D0%AE%D0%B7%D0%B5%D1%80%D0%B1%D0%B0%D1%80and look for yours in the left sidebar.
The usual size for a userbar is 350*19. The so-called "bigbars", with size == 350*40, were also popular, but did not reach the same popularity.
Userbars are still used in Russia, though their usage has "jumped the shark" since the most popular forums have placed severe restrictions on using images in forum signatures.