Coca Cola Tray - Signed

Dated 1936 - dusty and dirty. Been in my family for decades, but never thought to inquire on value. After some searching I've found this one a few places online but mine is the only I've seen that's signed and numbered.

McDonnelly #11 (or #4)

I was told when I was kid that it was the model's signature. I have no idea if that's true. Could be artist too. Im not expert, so perhaps one of you might shed some light.