I had that happen to me when signing up to vote. The elderly registrar did not accpet my illegible signature which matched the scribble on my driver's license upon which the rest of my identity was verified. I complied to get the darn thing out of the way.

On a side note, it was funny to see the registrars' walkers amassed by the registration table like strollers by the carousel at Disneyland.

Sixto