I can't speak to what is legal or illegal, but I can say that we have companies leave stuff in our neighborhood all the time. Some will place their business cards at our front door, some use door hangers with items inside. Some have dropped their business cards on our driveway in a small plastic bag with some rocks in it to keep it from flying away.

We even had a new Cleaners start in our neighborhood and they went around and dropped off really nice vinyl bags with their business card stating that they were offering a pick-up service and all we had to do was put our items in their bag on a certain day and they would take care of the rest.

I don't know if I have answered your question, but I did want to share that many companies do promote their services by putting business cards, etc. at the front door, by the mailbox and also on the driveway.

What I can't tell you (which I know there are great minds that respond in this forum, that can) is the ROI any of these company received using that format of getting the word out.

Good luck