State regulations require shoes and shirt when you enter a public environment such as a restaurant. To that end, a sign is usually found toward the front of the store, insisting on such compliance. Jimmy John’s Gourmet Sandwiches chooses to use humor to get people to do what is required. It aligns well with their brand and culture which has humorous signs throughout its decor.
Go back to a hotel or public pool you enjoyed as a kid. Nearby was a sign probably listing at least a dozen rules on them. Did you pay attention to it? Probably not. And you were surprised when the lifeguard then blew the whistle at you. Much better to get people’s attention in a positive way, than to create some rote sign and expect compliance by it merely being shown.
Providing great customer service is often impeded by the reality that sometimes we have to ask people to do things they would rather not do. The question is how do you create compliance other than using stiff enforcement tactic? I think humor or encouragement is often a better way to guarantee compliance, rather than stating signs and posting guards.