awesome idea, the only issue I imagine is getting too specific with the item - then of course all of a sudden multiple people have lost that very item.
when I was working in a school recently for example, I found this badass flashdrive shaped like a surfboard, unique to me had never seen one. So I posted a note on my classroom door like "Lost flashdrive? Consult with <my name here> for details".
Sure enough a couple of different students came to me "You have a flashdrive?" I say "Yes, what's the one you're missing look like?" and since none of these kids told me it was a little surfboard that came apart, I knew they were most likely trying to gank it. I have seen the same thing many times posted at trailheads etc. in National Forests "Found carkeys/phone/wallet - call <<number here>> and tell me what it looks like"
So people gotta be strategic and only adumbrate the details of the item itself on this public forum.. while being very specific with the location… maybe someone finds it paranoid thinking but I think it's realistically important