Affiliate Marketing Secrets

So someone not affiliated with USPS keeps leaving packets of ads in our front yard. One day, they apparently drilled a hole in my mailbox and inserted a hook into it to put their annoying ad packets on. I took the hook down, so they have resumed just leaving it in my front yard near my mailbox. But what I’m asking is this: Was it legal for them to put the hook in my mailbox, and is there anyway to get them to stop giving me these ad packets? I would leave a note, but there is no pattern to when they come.