I photograph in Sweden and the security guards are very nice! For example, there is a dirt-road to one of the runway's at Stockholm-Arlanda, which has a "no unauthorized entry" sign. Every day you see security cars driving on the inside and outside of the fence, to the approach lights and so on. When you are at the "no unauthorized entry"-road and photograph aircrafts at approach, one or two security cars usually drive past, but they don't mind you as long as you're outside the fence. We often nod at them to say hello when the drive past us, and they nod back.
A friend of mine photographed aircrafts with a big telephoto lens which rested on one's shoulder, and a security car with a guard stopped by asking if the camera really was a camera - I guess it looked suspicious with that big "bazooka" aiming at the aircrafts at the end of the runway.
So far I haven't had any bad experience with security guards - while photographing aircrafts! Otherwise, uhm... well, that's another story!