It should be but it isn't. The government long ago set a date by which silver certificates to be redeemed and after that all you could get for them was FRNs.
My guess is that the thing was just an old FRN. I've never seen a silver certificate for more than $10.
ML/NJ
>> “I’ve never seen a silver certificate for more than $10.” <<
From 1934 to 1957, all paper money was silver certificates.