I had already tried regular Sharpies and the ink beaded up and smeared off.

Most cleaners, soap, detergent, etc will not remove the ink from these markers.

The ink isn't perfect, but it's vastly more resistant to heat and solvents than other markers.

I found that most orange citrus type cleaners will take this ink off, which surprised me.

The ink is even more durable in ruff conditions where wear & tear might cause it to not hold up

Excellent, the best indelible ink markers I've used.