bicycle most likely, but could have been used on a very, very early motorcycle....like pre-1905 or so
send a picture to Jay Leno, He would know and he's a good guy Or Pete Eastwood, he's on here, and very Knowledgeable And also a good dude..
I don't think it's for a bike or a car. It appears to be an old railroad conductor/engineer utility light, like a flashlight ,before batteries were used.