This looks like typical marks from chain drop, and I wouldn't worry. You might touch it up with some paint or nail polish, but it doesn't matter either way. The BB shell is an area with plenty of meat, and failure is unlikely, and even if by some fluke it does fail, the consequences won't be any worse than having to walk home.
BTW- most of this kind of damage doesn't happen when riding, but when working on or transporting the bike.
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