What is a bamboo tattoo?

Well, a bamboo tattoo could be a tattoo of bamboo on the skin, but I think you are probably referring to the old way of tattooing with sharpened bamboo. The Word tattoo comes from the Polynesian Word tatau, which actually means to tap repeatedly. Still used in these modern times, but not so much, the process involved fixing a sharpened bamboo point to a flexible bamboo piece that was then tapped repeatedly with yet another piece of bamboo. This same style was used in other places with anything that could be shaped into a point, even rose thorns.