As an Italian I find the debate a bit surreal. In Italy a person is a suspect by default, and in a court one has to demonstrate to be innocent, not the other way around. This said, it easier  not to provoke the cops and get in trouble (which means that you do as they say, even if they are worng, especially if they are wrong and in a foul temper) .
I took photos in places where pople might react in a hostile way, such as Northern ireland during the troubles, or in Latin America. Here I live in a street which has been nicknamed by the local media 'The 200 metres of Fear' (I bit exaggerated but it gives the idea). I took shots in the street of cops and pushers, not blatantly, but not sneakily. Being sneaky it's what makes one suspicious. However, having a good story ready is very important. Sometimes it's even better one almost true. It gives you even the chance to say: I'm taking a break and I'm willing to have a chat with you. To establish a friendly realtionships, to lower the level of anger, hostility and fear is imperative especially if the cop is raw.  It has always worked in my case: collaborative, easy-going and smiling (not too much lest they think your making fun of them, especially if it's true).
Ciao,
Sandra