Looks like half of a plastic closure for bags of bulk candy, such as hard candy. There's another piece to it, a little "collar", that the point goes into and the teeth lock it when you slide it up this piece. The pointy thing ends up sticking out and was used to hang the bags of candy in the store.
So you fill your tall candy bag to about 2" from the top, then twist the top to close it. Then bend that twisted end around the squarish end of the closure. Then insert the pointed end into the collar piece and slide it up till it locks on the teeth. You can then hang the bag from the pointed end. To open, slide down the collar and remove the closure from the bag.
I haven't seen these in a long time. They commonly held plastic net bags too, like what you would see marbles selling in. I tried to find one in use for you on Google images, and there weren't any... just twist ties!