Why do police college students call them brothers and sisters?

Unlike the seniors of non-public security universities, more than 80% of the graduates of public security colleges have to go to the public security system because of their professional policies. In public security practice, they are all brothers, because the jobs they are engaged in after graduation are basically the same. The public security majors in police colleges in all provinces only recruit local household registration, and the public security work is closely related to the local dialect, so their sense of identity is stronger than other colleges and universities, and the habits of brothers and sisters have continued.