Well; I too would enjoy returning stuff left behind by folks on the river bank but it seems most everything I ever find is worm containers, bottles/beer cans, Mepps spinner packages and other trash....
Rarely however do I find items identifiable as post consumer fly fishing trash... like tippet spools or leader packaging.
Two weeks ago I found a large mepps spinner stuck in my right shoe lace up on the Soho; I will not seek the owner as I'm not as righteous as Shawn. LOL
On a more serious note I agree that anything you do (or say) that violates your conscious should be a clear indication of sin.