Use a jiffy marker. If you want to buy high speed tags, go ahead, but remember that on course, everyone is the same, so you might find yourself removing them in haste with your gerber. Also, you are unlikely to get through BMQ/SQ/BIQ with all the same kit you started with. Some will wear out, get ripped, etc, and you may even lose some (keep a grip on your kit), so you may lose some of those fancy tags.
But don't start randomly writing on your kit. Your name and last 3 of your svc number should be written in a spot that is hidden. As well, you don't want to write it on a place that gets worn down (like the bottom of your canteen cup). You will be told when and where to label your kit, hopefully by your section commander or 2IC. Unless you've been told to label your kit, but were not told how or where, wait out.
Good luck on course.