"My feeling is to do nothing. They cannot hear you and you are just adding clutter to the already busy channel."
Ditto, they can't hear you, you're just adding ineffectively to the racket by announcing that someone has an open mic. I assume that the USCG only makes announcements regarding an open mic to appease those that feel that they should be "doing" something about it. It's very frustrating to listen to, but adding to the problem doesn't help.
SV Laurie Anne
1988 Brewer 40 Pilothouse