This is marketing that customers see right where they buy. TV and newspaper advertising generally requires a time delay between the time the customer sees the ad and is able to buy.
POP has the advantage of being immediate.
A small sign at the cash register of a store can greatly increase sales. Other common POP marketing strategies include putting small signs on key products and stacking products in bins to encourage customers to dig through them. If your location gets lots of foot traffic out front, try moving signs and items out where passing pedestrians can see them. One of the great advantages of the Internet is that everything can be point of purchase. The customer sees a product, inputs their credit card info, and buys the product - all in less than a minute or two.