I know it's the complete opposite of summer right now (at least here on the east coast of the US) but I saw this and wanted to share. Valentine's Day is fast approaching;) Might make a good gift for a friend. It's a bikini bottom that gives you a little heart on your lower left side when tanning. Via Kiskin.it. You could totally DIY this yourself and make anything. Your initials, your beaus initials, a star, a music note.
I would think to do it you'd have to have something sturdy for the heart shape. Something like the material used in the LiveStrong bracelets. Maybe a sheet of rubber silicone (like this) or one of those silicone gel insoles for shoes (which might work better because they stick a little bit. Use a cutout tool (like this Martha Stewart heart punch) or a Sizzix heart die to make the shape. Plain scissors would also do. Cut outside into a circle and attach to swim bottom. I might try the heart shape come July.