I'd be po'ed if someone came on my porch to leave a flyer of ANY kind. That's trespassing. But I wouldn't go to the cops about it. I did yell at the guy coming to my door selling meat, though. Now that's odd.
I think if it's not posted as such and they don't have to go through a gate it's not legally trespassing.
But once the no trespassing sign goes up and they ignore it, I say turn the garden hose on 'em.
I buy meat from a guy that works out a pickup truck. The meat is better than anything in the stores and it is less expensive. Give it a try!