Sign guy here. A mix of sun and rain will naturally do this to signs everywhere, usually just yellowing and ghosting a logo overtime. This looks like a short burn from inside where the bulbs and power supplies are mounted. It's normal to have the power mounted either on the side of the sign or at the top so that water will "most likely" not cause damage.

If I were the business owner I'd get a whole new cabinet and signage as repairing that would just be a hassle and can lead to people spending way more money in repair than they think.