Pineapples specifically are the code for availability to swing. A pineapple print Hawaiian shirt would also work. If you see a house with a bunch of pineapple decor, they might be a swinger. Or they might just really like pineapples. Regardless, I personally can't look at the ubiquitous summer pineapple decor for sale in stores the same way I did before I knew about swingers and pineapples.