Don't believe the other guy. There are no watermarks in comic books like banknotes and stamps. There are several ways to determine if a book is original or just a replica. I will just enumerate a couple of the more obvious signs: 1.) Look at the indicia. It is usually found on the lower part of the page on the inside front cover or the splash page (page 3). There, information about the comic (volume and issue number, cover date, publisher, etc) are written. 2.) Check the advertisements. Does it look like the same age as the comic? If a 1939 book has a 1989 ad, then that book is definitely a reprint. But in some cases, old ads accompany the reprint. The publisher, however, includes a line above or below the ad saying that it is part of the reprint. 3.) The size is also a dead giveaway. Golden and Silver Age books are smaller than the original (they are wider). So it is important that you know how big a comic book is from a certain period to determine its real age. 4.) Compare the cover from a known original. It's not always the exact same cover. There are minor differences to differentiate a reprint from the original. The one dead give-away is the cover price. Surely, a 1950 book will not have a cover price of $2.00. There are more indicators, but these are the basic ones.