Was this a marking compound on anodised ally? There is no ways that laser engraved anodised ally (leaches the dyes) can have the lettering "rub off"
Most anodising has a sealant applied - the anodising is merely a porous layer that absorbs a dye (to colour it) and then is sealed after colouring. If you used a marking compound on natural (which is still sealed by not dyed) then you might have had issues with the sealant not allowing the mark to be truly permanent.