I velcroed a tile on the back of my sparky. The tile loves 2 ride on sparky's back wherever it goes. Luckily I have not had to actually use the tile but if I ever do, hopefully it will lead me to my friend sparky.
As soon as I got my spark I put a return mail sticker on it and then a piece of Scotch tape to waterproof it. I have that on all my quads and my RC airplanes just in case