Disliking tattoos as I do, I’m surprised to find myself suggesting today’s invention.
It’s simply tattoos which are drawn (inscribed?) as a stereo pair. Each image would be of some favoured 3-D object seen from a slightly different angle, so that people could ‘fuse’ the 2 images and see eg a 3-masted schooner sailing across somebody’s backside.
For those people who haven’t yet learned how to fuse two images, by slightly crossing their eyes, it would be possible to tattoo one image in red, one in blue and then view them through a pair of colour-filtered spectacles.
Certainly a talking point at beach parties, athletic meets, biker rallies and high-security prisons.