A customer display is used to provide information to the customer. This could be anything from the price of an item to the total amount or change due at the point-of-sale, even small advertisements or greetings. Customer displays are often used in grocery stores, drug stores/pharmacies, liquor stores, and convenience stores, among many other types of applications.
Customer displays are primarily used to display item pricing and subtotal/total amounts at a cash register. For example, when you are paying for items in a grocery store, the customer display often shows the cost of the item that was rung up, a subtotal at the end of the transaction, and the amount of change due to the customer.
Customer displays are also used to display promotions, greetings, or even just the name of the company. Most closed registers will display a short message to that effect.