without using high tech gear is probably the signal mirror. You don't even require a genuine "mirror" to send a flash type signal. Almost any flat or semi flat reflective surface will suffice.
While smoke signals are effective, they require work and fuel and most importantly, good timing. If your fire is not lit or your smoke generator not ready when the air traffic passes within sight, you're done son. Of course you might just keep a fire blazing at all times...good luck with that if you're hurt or weak or in an area with predominantly green, damp foliage. In short smoke just doesn't always work. Not to mention it is resource and labor intensive.
Fire is GREAT at night as a signal, in fact after the sun goes down nothing is better for getting you spotted. It would be hard enough to fuel a "tall" fire all night, can you imagine how much wood you'd need if you were making smoke all day AND fire all night. Save the wood for night time.
Pyrotechnic devices are wonderful but finite. I don't know how many flares you carry but let me tell you, I don't lug more then I have to so the flare gun is often left behind unless I'm in the Adirondacks or winter hiking in the Catskill high peaks region. Moreover these things are semi high tech, restricted in some areas and they can be dangerous at certain times of the year.
The flash of a signal mirror has been seen from miles away and in fact has been spotted by commercial aircraft at nearly a hundred miles away. On sea, (note: The horizon is 15 miles away at sea level) nothing is better for getting a pilot's attention.
(except perhaps the sucking sound of a Canada Goose passing though your intake fan) My Hat is off to you Sully..........just a damn fine job! I'll bet you made it onto allot of Christmas card lists.
Be improvisational! that's the secret to getting through a survival situation. Like the man said:
Improvise-Adapt-Overcome........say thank you and pay the bill.
Hold your reflector up to your eye and if you have one, site through the aiming hole towards the target (if you have no hole just site over the reflector) With your other hand, hold up two fingers (I use my entire hand) and "capture" the flash on your hand so you can tell the sun's reflection is pointed the correct direction. Move as needed until the target and the flash are in your line of sight. Sometimes I just use my hand like the shutter of an Aldis lamp and cover/reveal the flash towards the target.
DO NOT HOLD THE REFLECTOR STILL! move that puppy a bit. A steady stream of light may be seen but an EPILEPTIC flash is an attention getter. Practice in the yard. Pick a target to be the search aircraft (or distant vehicle / SAR team member) and practice finding your flash in your hand (capturing the sun) and moving it onto the target. This is not hard to learn or do but the time to try it is now under controlled conditions not the day you break a leg on a steep hill side.
Just another quick note on signal mirrors: Remember they need the sun, as you can see in the video they can still work on a cloudy day BUT you will need some rays to filter through for the best reflection. Ambient light just doesn't cut it. They may be used at night with an artificial light source. In this way you can "aim" your campfire light at a distant plane's blinking lights.
And finally be careful when you practice with signal mirrors. They are after all as bright as the sun. NEVER point them at passing traffic or in bystanders eyes. This can not only be distracting but could cause serious retina damage.