Here is a nice looking Herschel Walker autographed card, which I'm pleased to add to the Herschel Hoard, after a lengthy search.
This is from the 2011 Upper Deck Sweet Spot set. There was a set that contained NFL rookies of that year, and also a subset of college legends, called Veterans Signatures. I believe there were 49 cards in that subset.
The cards are different in that there is a raised plastic helmet on the card surface, which each player has signed.
Each of the cards in this set is serial numbered to 50, with this example being #13.
The back of the card looks like this:
Herschel also made the cut in two other subsets. The first is called Veteran Signature Variations. These cards are serial numbered to 30. The second subset is called Rivalries Book Cards. This set features two college stars from rival schools. In Herschel Walker's case, he's matched up with Bo Jackson from Auburn. The dual autographed cards are serial numbered to 25.
I hope to be able to add one or both of these card to the Herschel Hoard in the future.