Here's a Carlos Lee that is an obvious fake at first glance. Every letter is written out legibly, and in completely different handwriting than Lee's. Whoever forged it, tried to copy the facsimile signature thats printed on the card. But Lee hasn't signed like that since signing his Topps contract in which the facsimile came. This one is so bad, I can't give details as to why its a fake Like I usually would. So instead, its pictured here with an authentic one so you can see for yourself.

This one, I was told was an "early signature" and was one of the first auto's I ever bought. The first thing that jumps out at anyone, is there are 2 dots. As if its spelled with 2 I's. The C doesn't match any authentic one's I've seen. And the R has a small loop in it, that no other Ripken I've seen has. The J is just a completely different shape. Not to mention that Cal only signs his name as "Cal Ri J.(always has a dot at the end, which this one is missing)." I haven't seen any early signatures, so I don't know if he signed the full "Ripken" back then or not, but I am 100% he wouldn't completely change the shape of the 3 biggest letters in his name. the C,R, and J are all very different.

Here's two of the same guy. Both Fakes. The first one, I have no idea about. I've never seen any other Gwynn signature anywhere close to that one. Its SO different, it makes me want to believe its real. The Second one, Is actually a half-decent fake. Looks good at first glance, but when you compare it side by side to as many authentics as you can, you notice that the main thing wrong with it is the flow of the marker. This one is much more cramped than Gwynn's real signature. Especially the "T" and the entire last name. Also, all of Tony's Y's have a very slight bend or almost a hook backwards towards the end of his name. This one is too straight.
Overall the entire signature is too cramped, and has a different Stroke on "ony" and "wynn" than a real one would have.

The main thing wrong with this one, is the Last name. Simply put, its mis-spelled. In every Niekro signature I've seen, the "ie" is always separate from the other letters. Like, "N ie kro." This one is ACTUALLY spelled, "N W sii." Niekro ALWAYS has the "IE" clearly legible. This one, combines the "IE" with the first half of the letter K. so it looks like a "W." This is noticeable under close inspection, with visible pressure points. The rest of the K, is written as a lower cased S, followed by what appears to be 2 I's.
In the First Name, the P's inside loop is too large. Authentic ones have a more cramped look.
Overall, the signature doesn't flow like it should. It seems too, upright.

This is one I got in a trade. I am fortunate enough to have a certified version to compare it to.
The first thing to notice, is the "F". An authentic signature has more of a hook inwards at the top, and more of a flat tail at the bottom. It doesn't hook Upwards like this one does. The next obvious thing would be the large loop in the middle of the autograph. An authentic one is much more cramped, and actually comes to a point. Another obvious difference would be the end of the signature, how this one almost looks like the "@" symbol. Liriano's actual one does not have the smaller loop inside of the bigger loop like this, nor does it drop through underneath his Last Name like that.
Now, the not so obvious part, is the rest of the signature. The scribble in this one is actually quite different than any other Liriano I've seen, its just not as noticeable as the big parts.