Dive shop and travel agency customers asked us for a pen or marker that they could use to write on the back of our plastic luggage and scuba equipment ID tags that wouldn't smudge or rub-off when it got wet or spent considerable time under water. Until now, we have not been able to recommend or offer a solution. We were thrilled when we came across these oil-based, fine-tipped markers from Sharpie.
All of our laser engraved tags have either a black or white plastic back that can be written on with these markers. See actual sample below. We currently carry yellow, red, black and silver in ink-colors.