Do things in patterns of 3's. 3 stones, 3 whistles, 3 yells, 3 beatings on a tree. Do it in rapid succession.

When communicating by radio, do everything in 3's, as a station some distance from you may hear your call.

1) Call "MAYDAY" 3 times
2) Give your location 3 times
3) Call MAYDAY 3 times

Wait.

Repeat after 2 - 5 minutes. If you are transmitting on the same frequency as someone is sending, they cannot hear you. Wait until they have stopped talking. I think there is a "standard" to make your calls on the quarter hours also.

Other options if you have illegally modified equipment:

Transmit on the following frequencies could get you help quick(only VHF-Low and VHF-Hi):

American Red Cross: 47.42 (Channel 1 Nationwide)
Police Emergency Nationwide: 155.475
Search and Rescue (EMS) Mutual Aid: 155.295
Statewide Common: Varies
County/Parissh Wide Common: Varies
Amateur Radio: 50.125, 146.52
FRS: 462.5625 (Channel 1) (GMRS Shared freq)
GMRS: 462.675/467.675 (If only simplex, transmit on 467.675)
Marine: 156.800 (Channel 16)
Air Band: 121.500(Emergency Guard), Unicom (varies by airport), any VOR frequency that aircraft would normally use in the area.
National Weather Service: 162.400, 162.425, 162.450, 162.475, 162.500, 162.525, 162.550
Any nationwide, or locally monitored military frequency

If you have to make a call on one of these frequencies, you're probably screwed. <img src="/images/graemlins/smile.gif" alt="" />