maybe the wheels in the mill are from an OCD geometician that was practicing his tag - but spraypaint and markers were a ways off, so he grabbed his dad's compass on the way to school in the morning?

they hardly look like a rossetta stone to unlock the secret geometry or layout formula of a building.

why would they be on the interior of the siding?

my guess is they have little to do with building, and more to do with potential superstition or some f'ng around by the crew while the boss was chatting with the client.

were some of these used as maker's marks? (not specifically the mill's)

i know of a mark that i branded, etched, and scratched on furniture, some poorly thrown ceramics, and 2 timber frames that i've crafted. i only hope that they receive this much attention a hundred or two hundred years out.