I would say you can observe body language in some people to determine depression, but not all, by a long shot. You can also detect depression in some people (not all, again) by the color of clothing they wear: if they prefer black uniformly or purple, or
navy blue, that is an indication of depression. Bright colors such as red, yellow, orange, white tend toward happier moods if an individual dresses primarily in bright colors.

Purple and black used top and bottom are usually strong indicators of depression in
some people.