Jackpot!
You found what strongly appears to be an unlisted
retained Cud (the new lingo is "pre-cud") on the lower right wheat stalk. Your coin would be the first listed 1926-S RCD. There is also a die break on the left wheat stalk, but it hasn't completed to the rim or displaced yet.
Here's an enhanced version of your reverse photo, showing the RCD:

Here's the
link to submit your coin's photos to cuds-on-coins for attribution and possible listing.
Congrats on the potential plate coin!
BTW, I think the obverse gouges
could detail the coin. That said, I'm at VF-35 straight grade here. With an RCD plate coin, I'm not sure grade would much matter. JMHO, but if cuds-on-coins lists it, ANACS would appear to be your best bet for grade and plate coin designation.
Cool find!