No, Guy, you and Pappy got it the first shot!
DING! DING! DING!
It's a check punch, also called a check protector or check perforator. Technically a check punch produces holes in the shape of numerals, while a check perforator produces those same numerals via a series of small round holes, but essentially they serve the same function - to make it difficult to alter the amount of the check.
Basically it's a specialized typewriter, the best-known brand in the late 19th century being the Protectograph.
Good job, guys! I see I'm going to have to work a lot harder to catch y'all ...