Laser engraving is a great option as the way it works on anodised ally is that it actually just leaches the dyes out of the anodised layer (anodised ally is coloured using dyes that soak into the porous anodising leayer) leaving a high constrast almost white mark. it does NOT burn thru the anodising layer at all and expose bare metal thus you still get all the protection of the anodising itself.