Mike - I spent a couple of hours this week polishing and touching up an M64 I just traded into. So, I understand where you're coming from. The mark on your 915 doesn't look too difficult to cover up. I would try aluminum black first but it hasn't worked well for me before. Another thing to try is plastic model paint pens although it's prolly going to be tricky to match the finish on your frame. Last but not least - I just did this on a couple of (much smaller) marks on my LCP frame - you could try a laundry marking pen. Last resort - Allegheny Gun Works up in PA does actual re-anodizing and I've seen a bunch of comments about the quality of their work. Around $120 + shipping costs.