How to know if anyone has symptoms of depression?

Depression symptoms: 2 weeks or longer of mostly sad, low or depressed mood, decr or incr appetite, sleep disturbance, loss of interest + pleasure in usual things, crying more, guilt, fatigue, decr sexual interest + activity. Some medical conditions "look like" depression, and depression can be tied in with low thyroid or other abnormalities, so a good physical exam and lab work with your internist or fp is good.