From a reader:

Jonah:
Regarding your post:
“After all, we pay for our own “No Trespassers” and “No Solicitations” signs.”
Yes, we do. But let’s not forget that those signs would not be of much use without local no trespassing and no solicitating ordinances. That is exactly what the “do not call” law is. We must post our telephone number and, in effect, we are posting our own no solicitating sign for telemarketers.