Coin Silver Spoon Mkd J.W.JOHNSTON; John W. Johnston of Pittsburgh?

Offered is a nice American coin silver teaspoon marked J.W.JOHNSTON and also marked with a wheel-form manufacturer's mark often associated with Detroit. The only J. W. Johnston I've found is a jeweler working in Pittsburgh between at least 1863-67, and because spoons with this mark are sometimes found here in Pittsburgh, I've tentatively assigned this mark to that man. The marks on this piece are rubbed but mostly legible, and the spoon also has a period engraved script monogram of "LRB". It measures about 5 3/4 inches in length and weighs about 15 grams. Condition is good, with some minor bumps and scratches to the bowl, but no splits or repairs. All in all a nice presentable teaspoon with a fairly uncommon mark!