"Robert M. Gary" wrote in
ups.com:

Where have you seen that? All fields in Mexico have heavy military
presence, it would be very, very difficult to have an unauthorized
aircraft in Mexico. Even when you land at remote dirt strips you are
always greeted by the military. My plane is much safer in Mexico than
in AZ (statistically).

Evidently, it was a poorer attempt at humor than I had hoped.

The implication being that an unregistered aircraft might be in danger if it
were observed by a military aircraft near a Mexican border.