I recently took my bumper off and noticed handwritten numbers on a few parts. I know they used to do that in the "old" days but for some reason I'm surprised they would still be doing that now.

Here are some examples:

Behind the lower grille in the bumper:



In front of the front wheel below the fender:

 

Yea, I've still got some on my 08 GT. Most easily found on the trunks weather striping.

 

Yeah thats still pretty common especially with modern regulations. Could be anything from an employee of the guy that built or inspected or painted the part to a batch number. They use it for tracking mostly. That way if they issue a recall or tsb they can track the who what when and where of some of the parts. They also use it for warranty purposes that way if you claim something under warranty they can tell if the factory installed it or you did. Found a few on my brothers f150 when he wrecked it traced it back and determined it had been wrecked or at least hit during the PO's ownership as they were a much earlier batch number than his truck production date.

 

Thanks for the answers. Glad to hear they were factory "installed".