Found it? Receiving stolen property? $1800 bicycles don't usually go out and get "lost" on their own for you to "find" it. I would contact the police dept and ask what to do. If they want to impound it, I believe you can ask for it and keep it after the statute of time has passed. The police usually have an auction of found, unclaimed property anyway. You could post that you found the bike on Craigslist or such.
My friend had his over $1800 bicycle stolen from his house. We were out riding two months later and saw his bike. We literally took the bike out from under the person riding it and verified the serial number. We left with the bike and the dude who was riding was now walking. That could happen to you -- or get beat up by the person who owned it in the first place.