Banging on the Exit

Dollar stores value their shopping carts. So much so they corral them with vertical poles that prevent their being rolled out the exit. Of course, many shoppers attempt to exit with the carts. The poles hit  the top of the exit marking, scraping, and gouging the wall above the exit door. More wear near the center of the exit, less as the shoppers realize they can't leave with the cart and shove their eventual empty cart down the wall further marking its travels. A bell-shaped pattern of wear is left.