You're not the only one who dislikes those markings. Problem is, removing them may be more trouble than it's worth. If you want it to look right and have a flat surface you will end up flattening the cocking serrations. You could also grind off only the markings but be left with a dished area, visible if the surface isn't heavily matted. I might suggest just looking for another gun or slide with more pleasing rollmarks, or else just living with it as is.
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D. Kamm
USGI M1911/M1911A1 Pistols Website
http://www.geocities.com/M1911_M1911A1
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D. Kamm
USGI M1911/M1911A1 Pistols Website
http://www.geocities.com/M1911_M1911A1