I put a piece of painters tape on the part in question and write the date on it. I don't mind keeping stuff a while if it's not in the way, but when it comes time to do some equipment room clean up the date on it lets me know if it's time to throw it away.
I find a good bit of semi-valuable stuff at my car wash in the nice area of town around the vacuums and self serve bays. Some people just throw away stuff that I wouldn't- Folding chairs,working computer printers, etc. I suppose one man's trash is another man's treasure. Sometimes, it's obvious no one intended to leave it. A couple years ago I found an Iphone 4s. It was password protected and I couldn't get any info on the owner. I left it charged up and powered up so someone could call, but they never did. If I can't figure out by looking at the cameras and has no identifying marks on it all I can do is hang onto it a while and see if anyone comes looking for it. About three weeks ago I found a retractable step for an off road jeep. It appears new and they cost about $120. I really would like to return it, but you figure they give up looking after 48 hours. After thirty days holding time or so it will probably go on ebay.
You always have exceptions to people coming by quickly after they lose something. I had a guy come by one day looking for his lost floor mats. I told them I didn't have any by the description he gave me and asked him when he thought he left them. His response was "about a year ago". When I told them they had probably been thrown away many months ago, he got irate.