There's a public tennis court in the park and when I got there he was standing at the fence watching a girl and guy play tennis. The girl was cute and dressed in tennis clothes and he was really watching her not the guy.
After a couple of minutes he wandered over to where Roscoe and I were poking around in the grass.
I said, slightly shouty, "Hello, how are you?"
He said, "You see that girl there?"
"She's at the park all the time... playing tennis. I've seen her playing tennis with 15 or 20 different guys."
Then, he made a leery, knowing expression with wide eyes.
"She's the park slut."
I said, "Just because she's playing tennis with someone it doesn't mean she's doing anything else with them."
He then laughed like I had told a joke and said, "15/love! Love in the bushes that is."
Then he turned around and wandered off.
I am now convinced that the air horn is being used to signal the beginning and ending of "matches" downstairs.