I found the serial number! Or, rather, I found out that the writing scratched inside the folding hinge was, in fact, the serial number and not a previous owner's phone number as I had initially thought. I'm a little stunned that this is how Dahon was tracking their product—hand-scratching some numbers in the paint. But whatever, I'm just glad to know a little more about this weird bike.

Also, the first part of the number is H703, which I think means that it was rolling off the factory floor in March of 1987?