If one finds items with an identifying mark, he can presume that the owner has not despaired of recovering them, hence he has to announce the find and return it to owner. Examples include produce in a vessel, or a vessel as is, homemade loaves of bread, jugs of wine, and jugs of oil – these used to have individual seals. 

If one found behind a wall – which provides partial protection - young pigeons that were tied, he should not touch them. Perhaps a person put them there, and if the finder takes them and announces them, the owner may not have signs to claim them.