Interesting to say the least! I'm no pottery expert. Knowing where it came from might be very helpful and how it was found? Take this with a grain of salt, it looks like it could be an old colonial potters "makers mark", too bad there's not a little more there,very neat .regardless. I'm sure someone better informed will chime in.
Take a toothbrush and tap water to it. Don't scrub hard but just enough to get the creek stuff off. Before it dries take a pic camera on marco setting but with flash on. I will need to see the design and yes the state.
The composition of the pottery should tell you wether it is colonial or native american. Is it porous and look like it has white flakes mixed in the clay? That might mean native american. Colonial is often harder and brittle its a glazed type most times. It could also be modern porous exposed to the elements.
Is that a raised design or incised and scratched into it. Could be a mississipian era design but they were pretty random designs so you may not ever connect the dots. You should be able to determine if old real and native american though.
I'm 50/50 on it right now the outside says no the inside says yes haha Good luck!
I'm going to say colonial. The design is raised- it looks like, and I can see turning ridge marks on the inside (made when the piece was ion the wheel). NA pottery on the east coast is porous and usually incised with cord, corn, net, -- but pressed into it. JMHO Yakker
It's hard to tell a lot from the photo but it strikes me as a piece of Native American pottery we do find raised imagery on pottery down here it happens by carving the design or image onto a wooden paddle and pressing it onto the clay while still wet.. I don't know what area you're in but it might help you to look into paddle stamped pottery.
This is a check stamp design but it illustrates my point of raised ridges and lines