A good Sharpie will write on anything.

Marking Your Magazines

Marking your magazines, rifle as well as pistol, serves two purposes.  On the one hand, having them marked makes for easy identification and keeps them from getting mixed up with other shooters magazines.  But most importantly, it allows you to identify problem magazines and replace them.  Magazines wear out, and when they do, they cause malfunctions.

Regardless of the type of magazines you use, a good Sharpie Oil Based Pen will do the trick.

Another good practice is Marking Your Rifle

When they aren’t scrawling names on bathroom stall doors, Sharpies work great for marking magazines…