As far as I am aware there is no requirement to carry anything other than ones personal ID (passport/national ID card) and a licence to operate as a crew member on the aircraft.
Try telling that to the Frankfurt Airport security personnel.
therefore I have no crew tag, CMC or anything similar.
How do you operate in Germany? I went through Frankfurt this summer, full uniform, licence, ID, but they insisted on a CMC!
BTW, don't blame Jet Aviation as the security isn't controlled by them, this is also the reason why you will find differences between airports in the same country. However as I'm sure that Jet Aviation charged you a lot of money, it would be worth writing a letter of complaint to their GM stating that as a foreign operator using THEIR services, it was THEIR responsibility to advise you of visa issues and THE REQUIREMENT TO HOLD A CMC.
Mutt