I'm not sure how others would want to be notified of it, but I'd like to avoid bigger embarrassments, always.

I'd prefer to be notified as quickly as possible. I'd welcome being notified in the form of a quick "please check your zipper" leaning in closer, if a colleague or friend were to notice this.

I'd expect there's no need for making it more awkward by beating around the bush, sort of.

I've not had to notify others too many times, and I've not had such an error on my part many times either. So I'm not sure how well others will agree with my expectations.