Try to attract searches using their senses? here are some I can think of.

Sight-
flashlight, cell phone light, fire, bright clothes, messages left with cairns,
signal mirror, movement (waving), messages stamped in snow, items
left nearby (candy wrappers etc.), flares, email, smoke, footprints or ski
tracks.

Sound-
whistle, shouting, gunfire, car horn, cell phone, radio

Smell-"When I saw the flies, I knew I had found him"
smoke, decomposition, leave fecal material (this has happened on a search)


Other-
various beacons