From the photograph it appears that the blemish is corrosion of some sort. From time to time I've had similar issues with various firearms. For a blued revolver I'd suggest you try rubbing the spot with copper Chore Boy w/ some Kroil oil. Go easy as you can always repeat the process. There may possibly be some other method others might be able to suggest. HTH. Sincerely. brucev.
You didn't buy a "classic" to have one with a factory flaw. The gun has an MSRP of over $1000. Call or e-mail S&W, explain the problem and/or send a photo, ask for a box on their dime and and it back.
What you have there is pitting a localized form of corrosion that is pretty common with some blued guns. The problem is pretty common on the later S&W's with the shallow bluing, High Standards —which almost all had the problem from the 104's on or almost all of the recent production guns since a deep dark bluing process is too costly these days — it seems.
Anyway this type of pitting starts as ' Freckling' or small reddish dots or blemishes and once it breaks through the shallow bluing or oxide layer it comes back looking like a small crater with very rough surface. If you look at it with a 10X glass you will see what I mean. I can't see this as a manufacturers defect however it could be the fault of the retailers who didn't store the gun properly. This happens a lot with older guns stored away in cardboard boxes that get damp and/or pistol rugs that don't breath.
There is no full-proof fix for this. You could try Oxpho-Blue and oiling and it may work but there are tricks to using this stuff and practice makes perfect. The older deep dark bluing that used to be the standard had much less corrosion issues.