Assuming you want to get found, having accounted for all your more pressing survival needs, how to go about it is today’s concern.All other things being equal, if you were travelling in a vehicle, unless you’ve landed someplace horribly unsuitable, stay next to it or close by. A car, boat, or airplane is far larger search target than you are, and thus much easier for someone up in the sky to pick out down on the surface from altitude than your tiny body will be. Having it painted in a contrasting paint scheme like blaze orange or canary yellow is also a great help. I knew a boat skipper who’d painted his deck bright yellow, and the top of his cabin overhead blaze orange, because he’d taken the time to ask some helo pilots from the Coasties what would make their lives easier should they have occasion to come looking for him. A little bit of ribbing about his boat’s markings meant nothing to him, but being visible and recognizable should the need arise was a source of peace of mind on that score. If you don’t want a blaze orange car, consider a surplus parachute, or a poly tarp and some bungie cords to serve the same purpose on demand.
For travel on foot, a similar expedient can be arranged. A couple of yards of blaze orange nylon can be sewn or velcroed to one side of a military poncho liner, even doubled over so that if deployed it opens up to make a 5’x10’ splash of color on the ground, for a negligible weight penalty.
Next, you need flashier means to announce your presence. Being visible from 93 million miles, the Sun is perfect during daylight hours. The expedient of a small survival signal mirror, or even a car mirror yanked off for the purpose, gives you the ability to reflect the sun where you choose, as anyone who’s ever had some fun with a mirror on the beach at a friend’s expense knows. The type with Morse Code on the back and a convenient center hole for aiming the thing as you use it are quite helpful.
At night, your own sources of light project a long way. Battery operated strobes are readily available that are waterproof, and flash all night for 3-5 nights continuously on a single fresh D-cell battery. They’re small, so packing them unloaded, and keeping two fresh D-batteries outside, and popping them in as needed will prevent the misfortune of ruptured battery cells in a hot vehicle or stored kit. You can duplicate this capability with add-ons for common flashlights like Mini-Maglites, that’ll flash for you continuously, and have brighter but power saving LED bulb add-ons, in a smaller package.
Plan B is a flare gun and a collection of fresh flares for day or night, and pyrotechnic smoke signals for daytime use only.
Plan C would be a signal fire, with the means to make it smoky in daylight, or just burn continuously at night.
And for all events, if you can spare the cost, the gold standard is the newer line of personal locator beacons (PLBs) available at backpacking/sailing/flying websites/stores. Once registered, if you use them your personal data and precise location will be received by orbiting satellites, and transmitted down to the appropriate rescue organization to use in locating you and collecting you. Again, if you’re trying to be found, those are hard to beat. For those really seriously prepared, a handheld marine or aircraft radio are a fair amount of bang for the buck. I can’t guarantee that airliners passing overhead will be monitoring the distress/emergency Guard station (121.5 Mhz) for aircraft, but if the choice was trying it or not, I’d give it a shot. Someone 5-6 miles up you can talk to is always a lot closer than someone 10 miles away on the ground you can't.
By the same token, having a card with emergency numbers and an Iridium sat-phone means almost never being out of touch with civilization. Making phone calls from the middle of the Sahara is a novelty. Making them when you’re 40 miles from a trailhead and your leg is broken is a lifesaver.
A GPS or three comes in handy for the same reasons. Of lesser, but sometimes sufficient utility, are HAM and CB radios, and ordinary cell phones. Although for planning purposes, you may vary well need them most just after you’ve gotten out of range of anybody helpful.
The other caveat is that electronic devices will conk out just when you need them the most desperately, which is why I mention them last. The proper back up for GPS is a map and compass, and the know-how to make use of them at any time (I still rely on them primarily. GPS is nice, and I appreciate it, but overreliance on it will get one killed. Robin Williams’ routine about his car GPS advising him to “Turn Right Now!” in the middle of the Golden Gate Bridge is not only humorous, it’s instructive.)
And last of all, the humble sports whistle (ideally a pealess design like the Fox 40) will make a deafening amount of racket, and last far longer than your vocal cords will if you’re trying to let those within hearing know where you are. For the nylon, the mirror, and the whistle, and assuming you’ve already dealt with fire-making concerns when concerned with the shelter/warmth section, you’d be out of pocket about $30. Start throwing in pyrotechnics and electronic wondergadgets, and you could spend a few thousand.
So, the question comes down to where you’re going, and how much is your life worth?