Gizmodo's Sploid shares this handy field-guide to identifying drones (UAVs—unmanned aerial vehicles) overhead by their silhouettes from below.
It sort of reminds me how they say sharks target surfers because paddling, they look like seals to the hunter, rather than just a human meal of opportunity. One can find further details at the link, but I am sure it's not comprehensive and not like a bird-watchers' guide by virtue that these breeds are highly-invasive and don't stick to their native range and are prone to evolve pretty quickly. One can print the chart oneself or order it printed on mirrored foil, I suppose, to wrap around oneself as a cloaking-device when out and about, under the friendly-skies.
