Welcome to Coin Community, Annie219. Love it when new members post my favorite coin for their first thread. 
The mark on the reverse is a die crack. That's a fairly common location for die cracks on 1921's, and isn't necessarily definitive for that reason. Die cracks themselves don't warrant a VAM designation, but they can indicate a subvariety. Beyond that crack, I don't see any of the easy identifiers for a 1921 VAM, meaning this one would likely be a long and difficult process to attribute.
The mark on the reverse is a die crack. That's a fairly common location for die cracks on 1921's, and isn't necessarily definitive for that reason. Die cracks themselves don't warrant a VAM designation, but they can indicate a subvariety. Beyond that crack, I don't see any of the easy identifiers for a 1921 VAM, meaning this one would likely be a long and difficult process to attribute.























