Is there a building on the property? The tax assessor must have the right to go check out buildings on a property; they have sent me bills that included taxes on buildings and I never knew they had been on the place.

They don't like any sort of LEO. Who else would have the right to be on your property without any sort of permission?

My uncle got a big settlement from an oil company that ran tests on his land without permission. Timber buyers have been known to look over a place without asking and then try to buy the timber. These guys don't look like hunters, but unless they are working for govt in some capacity they very well could be up to no good.