I found this and two others similar the other day in Maine, and understand that they were railroad signs--I assume this one (with reflective circle screwed on top of the painted yellow surface) signaled "caution". With great heavily nailed and scuffed up surface, and nice yellow on yellow geometry, I like it as a readymade painting of sorts, good hung on the wall by itself, and perhaps even better with the other two! 

18" x 18" x 1 5/8". Super solid structural shape and what I think is quite a gorgeous surface. A hook or two or a wire could be strung on the back for hanging.