Hells bells. Dave is right, not a MayBell at all. It's much, MUCH better. A 1926-30 Gibson UB3, which is unmistakable.
Condition seems quite good, but the problem here is that someone decorated this gem. Even in the 20s and early 30s, the UB3 was an expensive instrument. Now, one in Very Good condition, which this appears to be, is worth about $900-1,200. The problem is that someone PAINTED over the sunburst and the Gibson logo on the peghead. I know that on occasion the craftsmen at the Kalamazoo factory added personal touches to some of the ukes they produced, and this kind of painting wasn't uncommon, but from what I see here, that seems very much unlikely, because the paint jobs are pretty amateurish - please, no offense intended!!.
My gut is that the value has been damaged somewhat as a result of the painting on the headstock and resonator back. To bring this up to full playability the vellum would need to be replaced, but the old one should be saved as a neat piece of period art. I'd say, in this condition, it could moved on ebay for between $650 and 750. I don't see many Gibson players jumping in with higher bids, but you never know. There might be someone out there who can't live without the artwork.
If you're going to keep this one, get a new vellum and set it. It's my absolute favorite Gibson BU, and most who play Gibsons feel this and the UB4/5, though very different, are equally excellent. What a killer find. Like Ukester Brown finding that Martin 3 in the trash!