I refute the "a good GM will" call, because there are as many personal variances on setting as there are GMs...
Sure, walking around downtown Seattle with an AR on your back is very likely to attract attention in most people's view of the setting, but that does not mean all. Nor does it mean that walking around with an AR on your back in Snohomish is going to be a problem. I'd encourage everyone to do away with the "a good GM will" arguments, because there's no such thing as an objective grading scale for what a GM should and should not to, only what makes the game fun for the group...
In one of my games, my character carries an Assault Cannon on the streets of Redmond (and quite possibly the outlaying areas). Sure, he probably won't be doing that if and when we get to Downtown Seattle, but I'd like to see anyone calling our GM "not good" for allowing that particular behaviour, and this game has gone from one end of the subtlety scale to the other from session to session.