Good idea about using the blue tarp for signalling. I find that anything blue on the ground catches my eye. I would guess that's also true from the air.

Vancouver Island is typically overcast during the winter. I'm not sure a signal mirror or even the glint off a windshield would be enough to catch the eye of a searcher.

One more tidbit relating to visibility ...

From globalnews.ca:
On Feb. 9, drivers from Gemini Logging spotted Henry on the road.

“Even the two guys from Gemini fallers, they literally got cleared to leave early,” Henry said. “They were like, ‘Man, if you were just moments slower, we barely even saw you. We thought you were a tree’.”