It is not a button. Beecause it seems to have a little stub of iron wire on its edge, it looks like a lead seal -- which is sometimes used as a sort of security-tag, like a wax-seal on an envelope. Among other purposes, lead seals were used on railroad boxcar doors. The seal was applied to the door's latch, and an unbroken seal signified that the cargo in the boxcar had not been disturbed. I think your seal MAY be a railroad seal, and the "C&F" letters on it are the initials of the railroad's name, such as Central & Frankfort Railroad Line. (That name is just hypothetical, because I do not know the names of railroad companies which operated in Indiana.) Please note, if your lead seal is a really old one, the company may have gone out of business.
C&F could also mean "Cost and Freight". [h=1]cost and freight (C&F)[/h]
Term of sale signifying that the price invoiced or quoted by a seller for a shipment does not include insurance charges, but includes all expenses up to a named port of destination.