I just heard someone hit their horn 3 times to alert a neighbor they were there to pick them up. They may have thought they were short, quiet honks, but they weren't. Honestly, because doing that in my n'hood isn't common, my first thought was that someone had a close call, so hit their horn. Nope. They were just announcing their arrival. It was jarring, and honestly, rude IMO. The person they were picking up has a driveway that goes right to the door (and the front door's about 25 feet from the street). And, the person they were picking up was already outside, waiting!
It may be common in some n'hoods, and it's okay if you don't have close neighbors you're disturbing, but if it's not the norm in your neighborhood it's just not polite. I have never had a visitor honk to say "I'm here," or "goodbye," and if I did I'd tell them politely that it isn't the norm where I live.