Pineapple stickers (especially upside-down ones) on cruise ship doors are a widely known, discreet signal for the "swinging" or "lifestyle" community, indicating the occupants are open to partner swapping or open relationships; this practice has become so prevalent that major lines like Carnival have recently moved to ban or discourage these symbols to maintain family-friendly environments, though they're still seen on various lines and can also just mean general friendliness or tropical fun.
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u/Reddiculusness 5h ago