Check this out! I just found this site:
martin info site
It had a great deal of info about Martin guitars and was most helpful in providing me with the information I needed to identify my weird Martin/Wurlitzer. According to this site's info:
"In 1922 to 1925, Martin made 297 standard Martin models (but with a simplier soundhole rosette) for Wurlitzer. These have the Wurlitzer name and model number on the back of the peghead."
My guitar does not have Wurlitzer name and model number on the back of the peghead. Instead it has the Martin logo stamped there and on the spine inside. Along with these marks is an oval shaped black and white Wurlitzer paper label glued inside the sound hole. It reads: Established in America Wurlitzer 1856.
The serial number on the neck block indicates this Martin was made in 1926. That's a year after they supposedly made them for Wurlitzer but perhaps why it doesn't include the stamp on the back of the peg head. Could it be that this one was a straggler, perhaps left over from an order already filled? Or maybe the info offered about this is a little uncertain.
The only other bit of Wurlitzer info is this reference:
"1922-1923: Martin makes guitars for Wurlitzer. Some lack Martin serial numbers or any markings of any kind."
I did some checking and according to the measures on this site my little parlor sized Martin is indeed an 0-18. This surprised me as I had already checked with a Martin dealer who told me that it's size did not match any standard body sizes Martin produced. I guess he was wrong.