When ever I had to fill in on a build team, I always signed the cars I built. It would ether be on the left or right rear frame rail, under the heat shield. (below the muffler) Although we were not suppose to sign the cars, it was kind of a "don't ask, don't tell" deal. I did sign under the hood of some cars, but they were special cars, and only with full knowledge of the owners and the powers that be at Ford. You would be amazed at how many people signed the cars they worked on. Most signatures would never be seen unless the cars were taken apart. It was more of a pride thing for us.
Even if no one else ever sees it, we will always know.