Green laser pointers are excellent signalling devices and should be included in any emergency survival bag, they are light and can signal aircraft and even others on the ground much like a flare gun.

when combined with Morse code you would even be able to send messages to others simply by shining it upwards in the sky at night and coding out the message.
obviously everyone would be able to receive the message and would see where it was sent from, but this is not always a bad thing, and for messaging over a few kilometres, would be better then a flare gun with only a few flares ..