Its a matter of expectations. If you expect any cop, big city or otherwise, to be friendly to you if you walk up to him on the street and ask him about his gun, then you will probably be in for an unpleasant surprise.
I'm not in uniform, but on occasion people who know what I do will ask me about what gun I carry. I've posted pictures of my carry guns here. In this setting, or with someone with whom I've had some kind of conversation, its no big deal. But if you walk up to me as a total stranger while I'm eating breakfast with my jacket off and ask me what kind of gun I'm carrying I'm going to blow you off. Sorry. Its creepy.
In one of Joseph Wambaugh's early books, either The New Centurions or The Blue Knight, a veteran cop tells a new guy his rule in dealing with the public - "Civil to all, courteous to none." This was about 40 years ago, and things haven't gotten any friendlier since.
I don't know SaxonPig, but from his many postings here he seems like a great guy. I would love to sit down with him and talk guns way into the night, and I'm sure I would learn a hell of a lot more from him than he would from me. But under the circumstances he outlined in the original post I'd probably respond in much the same way the Chicago copper did.