Well they _are_ guard dogs he he. Quite a different role than those that go out on recon and such. They're much more friendly to those they recognize as part of their "pack". Depends on what the mission is they're trained for of course.
BTW, I train German Shepards in the initial training they get before going off to more specialized schooling for law enforcement agencies here. Most of the police dogs in this county and several more throughout the state are dogs I've either bred or trained or both. People still have the idea that they're dangerous. Police here now drive the K-9 units into parks and such and have a "meet and great" with the public so they can be assured that the dogs are just as friendly and just as professional as any other law enforcement personel. You wouldn't mess with a policeman engaged in his duty neither would you with a K-9, but just as you can say "hi" or give a friendly wave to police (at least we do so here) you can pet a police dog that's not on duty as long as his handler is aware of your intention.