An absurd(ly) simple surveillance tool?
Today I was in Prospect Park after sundown. I saw something making its way across the sky above the Great Meadow with onboard lights, and since I've seen several UAVs flown by hobbyists recently, I thought it it was one. A few minutes later I saw "it" again - and then quickly realized it was a jumbo jet taking off from JFK - not a drone.
Then I realized with some optical trickery it might be possible to do inverse: a miniature 2D facsimile of a jet as viewed from underneath (that is the angle we see if from when standing on the Earth) and attach it to the undercarriage of a drone with rigid spacers. It would be a cheap, amusing, potentially convincing decoy or disguise for a drone crossing a crowd.
Things to consider: the altitude and trigonometric angle of the drone as calculated from an onlooker's vertical angle-of-view. Would not be effective if someone was using binoculars or analyzing the sound of the craft. Also the aerodynamics might take quite a bit of tweaking.