The 'Please Call Key' by Noah Lambert offers a simple and clever solution to the problem of losing your key by having your phone number permanently engraved on it.
It's easy enough to return a lost wallet, but most people don't have any kind of identifying information attached to their keychains. What they do have usually includes other important keys or perhaps even something as valuable as a USB. The Please Call Key is cut from brass and the personalized numbers are engraved deep into they key, so that regular wear and tear won't be an issue, even though the key will naturally darken over time. Now, hopefully if your keys do end up getting picked up by a kind stranger, they are able to easily reunite you with your keys without any hassle.