On a cruise ship, the secret symbol of an upside-down pineapple is regularly used as a code for swinging or “wife-swapping”. In most cases, an illustrated and upside-down pineapple is fixed to the cabin door of a guest interested in swinging and partner swapping.

In the world of cruising, the pineapple—specifically an upside-down pineapple—is a well-known "secret" code used to identify members of the swinger community. People might wear pineapple-patterned shirts, jewelry (like anklets), or place a pineapple magnet on their cabin door to discreetly signal to others that they are interested in "partner swapping" or the swinger lifestyle. However, there is a lot of nuance to this: the pineapple has been a traditional symbol of hospitality and welcome for centuries, especially in the Caribbean and Hawaii. Consequently, many people wear pineapple-themed clothing simply because it looks "tropical" and festive for a vacation, completely unaware of the secondary meaning. If the pineapple is displayed normally (upright), it is almost always just a sign of friendliness or a love for fruit. The "lifestyle" signal is most specifically associated with the upside-down orientation. To avoid awkward misunderstandings, most cruisers suggest that if you just like the fruit, wear it proudly, but maybe avoid putting it upside-down on your stateroom door unless you are looking for a very specific type of social encounter.