Depending how deep the initials are cut in you could dimple the surface lightly with a punch, then peen with a hammer and get the metal all back together and then depending on how the rib is matted, (if the rib is North and South straight lines) you could file this area back in. I am doing a similar job on a barrel where someone drilled and tapped the rib. Filled the screw holes with screw peened and filed. It's tedious but can be done.