I've found two knives.
One was a Buck Alpha folder with black rubber handles. It was lying in the middle of the street in front of my job. It was in it's nylon sheath and at first I thought "Cool! I found a knife, my lucky day!" It became obvious that it had been run over at least once. It wasn't really in bad shape considering. The only problem with the knife was that the rubber handles had torn out from a few of the attaching bolts. The rest was unharmed, still opened and locked-up fine. I showed it to a co-worker, told him I didn't want it and he asked if he could have it. I said "sure" and he was thrilled, like I had just given him some kind of treasure. I didn't feel right about giving away a damaged knife so before I let him have it I took it home, reattached the handles, and replaced the damaged snap on the sheath. He was like a kid on christmas when I gave it to him.
The other time, I found a big SAK (a real one) at Home Depot. It was sitting, with the blade open, on top of one of those cabinets with all the drawers where they keep nuts and bolts. I figured someone, maybe an employee, used it to open a box or something and forgot it. I had no interest in the knife so I thought I'd score some karma points by turning it in. I walked over to the customer service counter (there were three employees there), put the knife on the counter (knife closed at this point), told them I found it and where. They looked at me like I just landed from Mars. They didn't seem to know how to react. They were clearly surprised. One of them took the knife, said "OK", and put the knife in a drawer. Only after I had turned around and had taken a few steps away did the one who took the knife call out "thank you". I think maybe part of their surprise came from the fact that I'm a biker, and looked like one at the time. There I was, a scruffy looking guy in a ragged leather jacket, ragged motorcycle boots, and a fixed blade sticking out of my back pocket, turning in a found knife. It was kinda funny.