Three loud whistle blasts is the simplest and most universally recognizable wilderness distress signal. Whistles are lightweight and easily portable even on a backpacking trip where every ounce counts. Wear a whistle around your neck for easy access even if you get separated from your survival pack in a fall or other accident.
Flares are visible from a distance to help airborne searchers narrow the search area. Check with local conditions and regulations before packing flares however as they present too much of a fire danger in some heavily wooded areas. If you choose to include flares in your survival kit, remember that they are only useful when you hear search planes nearby who may see them. Do not waste flares by shooting them off at random when no one is around to notice.
Brightly colored ponchos, clothes, bandannas, ground cloths and aluminum foil serve as flags to catch the attention of the search and rescue team. Hang them from trees where the contrast with the natural surroundings will catch a searcher's eye or lay them out on the ground to be spotted by airborne searchers. Hang a sheet of aluminum foil where it will reflect the sunlight. At night hang a flashlight where the beam will reflect off the shiny surface.
Light up your camp to make yourself visible even at night. In addition to flashlights and aluminum foil, hang glow sticks and flashing LED lights from the trees. Line tree trunks with reflective tape to catch the beams of searchers' flashlights. Use a signal mirror to flash light at passing aircraft. The idea is to make yourself as visible as possible instead of blending into the background.
Create even more light with a bonfire. This is effective for being noticed from a distance but, again, you will need to exercise caution before utilizing fire. Don't put yourself in worse danger from a forest fire while trying to extricate yourself from the predicament you are already in. While fire is easily visible at night, plumes of smoke will be more effective during the day.
A cell phone can be an easy way to simply call for help and let searchers know exactly where you are. In many backcountry areas however, cell service is unavailable. If you find yourself in imminent danger or a life-threatening situation, a personal locator beacon uses triangulation technology to get a fix on your location and transmit a personal distress signal to the National Oceanic and Atmospheric Administration and Air Force Rescue Coordination Center.
