Bava Metzia 27 - Are Identifying Marks Torah Law?

The commandment to return lost objects states "... and so shall you do with his garment...and with any lost article ..."
The garment is already included in "any lost article," so what does it teach? - Just as garment is special in that it has identifying marks and claimants (owners), so too, anything that has identifying marks must be announced. However, one is not obligated to return a lost object that the owner has despaired of recovering. 
Do we see from this ruling that identifying marks are from the Torah? No. The ruling may be mostly interested in the second part, owner's despair, and mention the marks only incidentally.