At the half hour call, I always say, "Ladies and gentlemen of the <name of show> company, this is your half hour call. If you have not signed in and read the notes, please do so. Half hour, please."
Sometimes not everyone signs in right away, so a reminder is not a bad idea. Then I go and check the sign in sheet and see who, if anyone, I need to call. The crew obviously knows this does not pertain to them, since they have gotten to the theatre earlier and already signed in on their own sign in sheet. I do, however, encourage the crew to read the notes on the actor's sign in sheet.
I find that making calls relative to five minutes and places muddles the information. Therefore the five minute call is usually five to curtain and places falls anywhere between 2-3 minutes before curtain.