I’m hoping that it’s clear that there’s a bell connected to the door of the diner. This is typical in the US (at least for older diners), but I’m not sure about Ireland. I know diners themselves aren’t typical for Ireland, but there’s a backstory to the Nighthawks Diner that will be made clear in the next story arc.
Follow this story from the beginning here.
Ballinabricky 
Over here in the Netherlands we do still see the bell around here. Sometimes in cafe’s, but mostly in small shops/ store’s (and my small town hairdresser 🙂 ). We don’t have typical diners though.
In NJ, there must be a diner for every inhabited square mile. Sadly, most don’t use the bells, either.