As a forum focused around ponies, most people tend to use avatars and signatures that revolve around MLP:FiM in some way. Not everyone, but most :3
On this day, you're encouraged to be a little creative; switch your profile around (avatar, signature, name, all of the above? ) to whatever you want; as long as it's not pony related. Have a favorite character from a video game or movie? Maybe another animated cartoon you really enjoy? Throw them up there for a day!