I've seen those (thumb planes ?) by a bunch of makers.... as usual, Stanley had it "first." But, Craftsman, Stanley, Sargent, Stanley Handyman , … after that every high and low class plane maker had them. I can't tell from the picture, but how "thick" the blade is can tell a little bit about it. Also, if the "thumb" part is completely smooth, more likely a Stanley then the others. That's my two sense... which may not make sense at all.