There have been some famous fakes in the sports card industry. A few years back there was a Babe Ruth, Ty Cobb, Walter Johnson and Honus Wagner card that came out of a pack of Upper Deck. It had 4 cut signatures. 2 of them were fake.
There was a 1928 Fro-Joy Babe Ruth set that was also a fake.
There are many more fakes out there and there always will be as long as everyone is looking for the holy grail of baseball cards. If we just enjoyed them for what they are and we were true fans and not interested in them becoming more valuable one day then no one would waste their time or ours making fakes and forgeries.
When it comes to cards be a fan and not a speculator.
Here are links to the 2 fakes I mentioned above