Depends on the bar...
Sometimes a bar will have a bell for some type of promotion. So when the bell rings - it’s on my friend. I’ll never forget the time I was in a bar in a neighboring city. All of a sudden a bell rang and three beautiful girls came out and poured shots directly into my friend’s and my mouth. It was unexpected, yet welcomed.
Other situations for a bell ring could mean that the bar just received a large tip. In this case, it acts as an acknowledgment or perhaps bragging rights for the service given.
For some bars, the bell is for help behind the bar. When a bell rings in this case, you might see some extra staff running out; literally.
For the most part, bells are a way to draw attention. They are an effective way to let people know that something’s happening. Whether that attention is directed toward the staff or the patrons can be up for debate.
However, I think we can all agree on one thing: MORE COWBELL!