Unlike my heroic brothers on the East, I just fly domestic. FWIW, when I can't hear the controllers anymore, I figure that's a good indicator that I've gone beyond VHF coverage. Hope that helps.
The symbol is "F.U." short for "frequency unavailable". That's when I pull out my sextant and start reporting my position with Morse Code via my on board Marconi.
Those other guys have it all wrong, it is directly proportional to how much aluminum foil you have on your head at the time to prevent damage from solar radiation and alien technoligies.