Yep! That's what was SO funny about it, that it was completely unexpected,
and "not correct at all". We closely examined them, compared them with the
pots where the lines are done the usual way (at Oklahoma's "Red Earth
festival I watched Acoma pots be painted using pounded pine needles but
don't know if that's the standard) and it's Sharpie for sure. The slightly
oily slightly gloss finish, too. And the lines turned out not to be so fine
on close examination - just, um, Sharpie width. The signature is exactly the
same "mark" as the lines - same width, same oily gloss.