A simple small punch mark. 'DT' ,,the T being part of the upright bar of the D.
A few Parkers got marked down in the dolls head seat in the frame. A couple of Winchester leveractions on the bottom of the frame. There's usually a small flat back by the trigger to place it. I can't ever recall a SAA or 1911 being marked. But it's been a long time since I was there,,don't know what they do now.
When I was there, he offered a small,,very small,, dollar amount off the final bill if you the customer allowed the stamp to be applied to the finished piece.
I don't recall anyone ever taking advantage of the deal!