Hi...This is a facinating topic...I wish I could help as far as resources, but... no such luck. However, I grew up with a father who was a cop (now retired Sargent) and my brother has followed in his footsteps (now a detective). The previous response was very heartfelt and I agreed with most of his statements.
I would like to add that (from my personal experiences)cops tend to separate from "general" society and limit their friendships to fellow officers. While I understand that there is a common "understanding" amongst co-workers, I always felt that my father and my brother lost touch with friends (who were outside the force)that they would not have if they had not become cops. They shyed away from people who would ask about'war stories' or 'needed some advice' or 'had a neighbor who...' because they wanted their job to be done when they came home.
Another aspect of a police subculture might be the trust factor that the previous person discussed. Might I add that cops tend to become paranoid as well. Given the nature of the business (putting bad guys in jail,) it was not uncommon for the bad guys to make threats, like "I'll get your family/wife/kids..." "Iknow where you live..." "Watch your back..." Or, like in my father's case, he would advise us not to drive certain roads because of a dangerous curve. He had worked many accidents there, many of which involved fatalities. Or, like in my brother's case, he would always ask about home safety (e.g. carbon monoxide) because he had worked a case where the entire family had died in their sleep.
I hope this info helps out... of course there is no scientific basis for my thoughts... they are just thoughts from my personal experiences.