OK, all your batteries are dead, how else can you signal/communicate? Morris (like the car?) code, semmafore or smoke signals. Morse code, you could use heliographs (mirrors) arms, flags. Figgure one system as right side-dash, left side-dot. Flags the same thing. Proably a standard system already exsists. Semmafore uses two flags and the position of the flags represent a letter or number. Used to be able to do this one, thank-you Boy Scouts. One thing to remember is that It takes two, at least, one to recieve and one to send. Practice practice practice. Personally I would rather use pidgeons or messenger rabbits for long distance. The rabbit thing was a joke we had about our neighbor being a Russian spy, had rabbits running around the backyard. Then one day two guys in a dark sedan showed up, asked to park in the driveway, never said who or why. Had badges and ID from the .gov. Hmm. True fact. Tin can phones? Gonna buy some monkeys and train them as messengers.