I always respond passively and these situations have never turned into anything too serious but most recently I have been asked by a female security guard from her squad car whether I had ever hear of Al-Qaeda when walking with camera along a side-walk near Dallas. I had taken a few shots of a bright pink sunset and she suggested that this was an abnormal thing to want to do so I should make myself scarce to avoid being taken in.
My attempts to get these folk to see the funny side of the situation seem to always fail though - maybe my style of humour is a very British thing ?
I worry one day that one day I might be accused of being Al Qaeda etc. I am actually of Pakistani origin and Muslim - I have brown skin and a foreign name. So far no one has ever stopped or questionned me. There are very few non-white British walking around with binoculars, cameras. I do think that if I am ever hiking in moorland one day some one might accuse me of "Mujahidin" training. The fact that some of those involved in 7/7 were doing all those tough sports in Wales and the Lake District does not help.
Maybe the fact that I actually belong to an ethnic minority on Britain would deter me form being harassed. They would hate to be seen to looking racist.