Laser engraved stone
Cheap (free!) and easy to work with, for jewellery and other crafty things. Excellent for weddings.
We can laser engrave any flat surfaced stone, as long as we can get it in the machine (10cm deep in the Epilogs, 25cm deep in the Chinese lasers).
You're not limited to just words, though they are of course popular. You can add images and logos too. It needs to be flat so that the laser power is even across the whole surface. As long as the area to be marked remains in focus, we can mark uneven surfaces.
Depending on the make up of the stone, it may mark very clearly or not mark at all. It's very difficult to advise as we're not mineralogists!