They are too light to be a weight and most weights have a ratcheting piece on them.
The other thing that makes me think that they wern't used to let you know when the machine is empty, is because the nickle fits in a slot and the nickle pushes the candy bar out when the knob is turned dispensing the candy. If that piece is used to block the nickle, there is no way for that nickle to be returned, making a customer angry enough to attack the machine.
The machine does have a rejector. When the last candy bar is dispensed a bar raises up which interferes with the coins path and sends it out the side.
I am puzzled what the purpose is for this piece. Hopefully, someone out there has one of these machines with those pieces in use. As Tim mentioned they are not needed for vending, but companies just don't throw in extra parts for nothing. Just curious.