1943 S OVER D?

[nohea]

I came across this and am not sure what is happening with this mint mark. There appears to be a curve to the northeast which may be part of an S or a D (or just a gouge) and a straight line in the lower part of the mintmark which could be part of a D (or another gouge). Am I looking (and hoping) too hard at this mint mark?
There were 5 nice steel cents (with a bunch of corroded ones) in the rolls and I was also wondering what would be the best way to preserve them?
Unfortunately it isn't copper, that is the way the picture came out.

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