Way back in the way back as Co-Pilot, I carried my logbook and had the Captain sign it after each trip certifying that I had acted as PIC for 'x' hours under his supervision. I don't recall now why that was 'important', but I have quite a few pages with signatures. Might have had something to do with time towards the ATR or something, can't remember. Probably doesn't apply any more anyway. I do know that after that I never carried my logbook with me.