How to identify plainclothes policemen

Plainclothes policemen are usually on duty or off duty. For people on duty, they are basically no different from ordinary people, but because they are on duty, they may not care much about things that ordinary people are interested in (such as watching the excitement) and concentrate on one thing. Being a policeman for a long time will have a different temperament from others (just like a soldier), which depends on your own continuous accumulation and discovery. Qualified plainclothes policemen should not be seen by us. I wonder if this answer is useful to you?