Made and marked by D&W Auchterlonie, the grip on this c. 1900 blade putter has an aluminum thumb guide nailed in place. The guide is stamped "Pat App For" and is nailed into place on the grip in order to set the golfers left thumb in the exact same spot. Such grip appendages were devised to assist the golfer in positioning the shaft in his or her hands. Golfers back then did not feel much of a need to use such devices judging from their extreme rarity today.
The back of the blade has a dot stamp which indicates that this club was inspected by somebody in charge after it was made. Tom Stewart would use a dot stamp as his personal inspection mark. Its possible that one of the Auchterlonies or both did as well.