Don't be surprised if your local shop has no idea what a Rockwell test mark is. Error coins are a specialized area and many dealers don't have the time to be knowledgeable about every subject. The great thing about forums like CT is the concentration of specialists from around the world. Whether it's errors, ancients, VAMs, or early copper, chances are you'll find more expertise here than at your LCS. Plus you got an opinion from the top error dealer in the world in an earlier post. Keep that in mind when you are explaining a Rockwell test mark to the dealer
I took an old coin to a deal. His thoughts (that is to say he barely took a second look at it), were that it was a toy, a token, worth nothing. Thinking he knew what he was doing, I threw it away, only to see a very similar picture months later of a great find from the Roman era. Oopppssss.