You may or may not have a written guarantee. However, if a customer calls you with questions or some problem with your sign, it is good business and good customer relations to handle both. Peeling graphics or faulty installation, for example, is a mistake. You can fix either with little or no problem. But the failure to do so could be a mistake you might never overcome.
Reputations are strange.
They are difficult to build and easy to damage. That is why customer relations deserve careful attention. Customer service is really the only way to go. Customers depend on you, and you depend on them. Do your job right, and the customers will do right by you.