I use nail polish to mark my metal & wood needles. It dries perfectly smooth with no drag and so far doesn't seem to be wearing off anytime soon. Nail polish may or may not stick to plastic needles, depends on the type of plastic. I happen to have some black halloween polish, so I used that as it shows up well.
I use either dots or the actual numbers. Smaller needles from size US1 to maybe US8 or so get dots. A size 3 gets 3 dots, size 4 gets four dots, etc. If the needle is big enough I just paint on the numeral itself, like 15 for a size 15, etc.
I do this on all my circs and dpns.
I have some sock needles but I don't bother marking them because they are too tiny and I rarely use them.