My father and I used to have a signal: call on the pay phone, let it ring one time then hang up...meant it was time to come pick me up from the movies or wherever...then I got the dime back! Take that AT&T
Another trick to let your family know you had arrived safely to your destination and give a message was to call home collect, ask for yourself with extra identifiers to convey a message...like a collect call to Joe edward blow the 3rd....