I actually already own a few cool proof cards, which might be worthy of a post at some point soon, and recently saw a proof which I could not pass up for less than $5 delivered.
1999 Topps Gallery Ray Lankford Private Player Issue Proof
The proof card is some sort of pre-production card used by Topps for something. I am not exactly sure what their process for making a set of cards is these days, but this card is in there somewhere. There are some slight differences between this card and the regular issue 1999 Topps Gallery Ray Lankford card. First, this proof card is actually of the Players Private Issue card, not the base model of the card. Notice the inscription in the top left-hand corner of the card showing it to be a Private Player Issue. The Private Player Issue cards were a parallel to the base set which generally ran at one per box with a print run of 250 per card. Here's a look at a copy of an Albert Belle Private Player Issue:
1999 Topps Gallery Albert Belle Private Players Issue
The Lankford card and Belle card are nearly identical including the Private Player Issue script in the top left-hand corner of the card. However, as mentioned before, there are two slight differences between the regular issue and proof issues of these cards.
First up is the difference in size. As you can tell, the Lankford card is both taller and wider than the Albert Belle card. It looks like a huge difference in this picture, and is noticeable when handling the card, but for the sake of storage the proof card does fit inside a regular top loader. My other proofs, I swear I will put them in a post this week, were big enough to frame and hang on the wall.
The second difference is in the serial numbers on the back of the card. The standard issue Belle Private Players Issue features the usual serial number written on the lefthand side of the card with the print run at 250 cards. The Lankford card however is a proof which means that it is likely a one of a kind card and features.....
Absolutely no serial numbers. The box for the serial number is on the card if you look carefully. Very happy with my new Lankford addition. Though a little bit of an oddball card a really cool and unique find from one of my favorite players. More proofs and Topps Vault stuff later this week.