If you have to signal someone and the aircraft or someone that's distant on the horizon, one of the ways that you can use the sun to signal is by having a reflective surface.
Right here, I have a mirror. You can also use something like a CD or DVD. That will give you enough shine to make a reflection.
The way that I use my mirror is to shine onto my hand--I don't know if you can see that shining on my hand--that light is what's going to reflect wherever I aim. If I use my thumb and my forefinger or make a sight right here between my two fingers, I can take that sight and move it to wherever I want to shine. I can make that shine in the direction that I want to signal.
If you were signaling an aircraft, you'd want to put the aircraft right here in your V and put the light on both sides of your fingers so you'd get that shine, and you'd be able to signal.