The ink used for marking pressure-treated lumber grades is a water-based ink that will naturally disappear over time from rain and foot traffic. You can speed up the process by scrubbing it off with a bar of soap and a brillo pad. If the mark doesn't completely disappear, you can sand it lightly with a palm sander using 150 grit sandpaper. Some deck builders also use a paint thinner to remove face stamps on wood.
Lumber Grade stamps can be erased with a little sanding.
