The most obvious sign is that they are satan. but there are other ways of telling, such as the cosumption of guenea pigs (this behaviour is excused in Southern America, becausethere aren't always enough gophers to go around), the ability to drink monkey semen without a twist of lemon, or the ability to fly like a penis on a motorcycle. watch carefully, and submit your entries to the guestbook.
Also, we have a bible called the Skabeeble

The Who Is Satan? Guestbook
When signing the guestbook, use: "Another Satan" as the subject heading to avoid confusion, and i will compile a list of satans below

View the guestbook here
Sign the guestbook here