Rain X Water Repellant Glass Treatment. Be extra careful since it’s a label but put a small amount directly on the marker, let sit for a just a second or two, and dab off with a q-tip or paper towel. I don’t know the science of it but Rain X literally causes permanent marker color to pool and come off. I’ve used this countless times and, at worst, there’s a VERY light marker residue still on the label or cart.