No " F " stamp and flying
I have flown into Germany a guite a few times, with and without the " F - as is Freed from the gun laws " Stamp. Getting into the country is no problem, as long as you are not dumb enough to declare the marker in your luggage that goes into the hold as a firearm, which always gets checked at arrival. Real Dumb - but I know of two teams which did this!!!
Flying out is the problem. Since 9/11, all hold luggage goes through an x-ray machine, and that is where the security guys get worried. Not because of the marker, but the air bottle, which looks like a bomb!!
The last 3 flights, I have always been called to the sec office, and have had to show them the bottle, and that is was open (no reg). the gun was always packed (wrapped) well away from the bottle, and have had no problems. My tip about the "F" stamp, when you are at the site, just go visit one of the german trade stands, they will most probably help you out. Whilst you in Germany, always travel with the gun dissembled.
So u there!!