Originally Posted By: Reddy45
If you can't find anything, I can vouch for using the $1 bottles of craft acrylic paint at Wal Mart near the sewing section.
On a previous vehicle I had a nail puncture a tire so I used a dot of gray acrylic paint to mark it for when I would take it into the shop for repair. Long story short, that acrylic dot didn't come off until I bought new tires some 30k miles later. It survived wheel cleaner, weather, direct sunlight, etc.
I have a HK USP that I dabbled some of that same paint into the rollmarks on the slide and they haven't come off in several thousand rounds. Through scalding heat and cleaning and oiling. Still there, like the day I put them on.