I have pretty good luck with just using a Sharpie to write on mine, it usually lasts a couple years before I have to go over it again. I mark my small red gas jugs for my 2 cycle fuel and I also mark my 4 different plastic garden sprayers for their various chemicals. I use the standard Sharpies that you can buy most anywhere but you can also find the industrial/permanent markers that might hold up even longer. One of my 2 gal garden sprayers I use for gly-4 is about 25 years old and you can still read the original writing I did on it way back then but if you want to remove it the old style brake clean or CRC lectromotive cleaner will take it right off without damaging the plastic at all. I always pre-clean the area with either of these before writing too.