And airlines get fined for every one noted by the Bundespolizei at the Federal border. Hence the airlines' specific interest in this area. Can't remember the amount, but I seem to recall 60€ a pop, United got a big bill recently, and almost as recently United staff got a reminder to check passports for this.

UK Passports used to have a box at the back of the passport for signing, but it long ago got photo'd in during the application stage, and should be clearly visible on the data page. I don't think there are any unsigned passports left now. Other countries still require a passport to be signed after delivery, and the German approach to this - which is so out of step with their laid back approach to paperwork - is that an unsigned passport is invalid.