Appropriated from: http://www.geocities.com/Athens/8580/counterf.html because the page has been down from time to time.
There are a number of slight differences between the real and counterfeit versions of Cerebus #1. Here is a listing of them, special thanks to Chuck Costas, Rory Root, John Tinkess and Margaret Liss.
Real: Has Silver staples.
Fake: Has Bronze staples.
Real: Inside cover is flat, outside cover is glossy.
Fake: Both sides of the cover are glossy.
Real: Cover background is pure red.
Fake: Cover background is red, but has a slight orange-ish tint.
Here is a big picture to better show the differences via the red covers.
Real: Cover is of variable print quality (sometimes "smudging" appears around the right horn on Cerebus' helmet and the hilt of his sword).
Fake: Cover is always crisp.
Fake: Sometimes a black outline can be seen at the bottom of the cover.
Both: Verticle black smudge line appears on the back cover where the "Collector's Edition" banner ends (because the book was printed "golden age size" when the artwork was intended to be modern age sized)
So if you have a very good-looking Cerebus #1 it may be a counterfeit. It's sad to say but there are counterfeit comics out there. Especially for high value independent comics. If you are thinking of buying one, check around to see if counterfeits were made (and how to detect them) before doing the purchase.