Not Sure What This Is.

Reminds of a checkering tool imprint. Used mostly on wood or leather. Thanks, Doug.

I lean toward post-strike damage for two reasons: (1) the shallow depth of the impression and (2) the presence of damage on the reverse face across from the obverse serrations. That said, I find the length of the "tank track" puzzling, as the impression of another coin's reeding should be shorter and should fade out at both ends. It's possible that a quarter was rolled across the surface under pressure.

I find it strange that the impression appears to curve slightly.