I have to add, watch out for your friends and loved ones. Some of the signs are not as obvious as you'd think, and it is a very deep hole out of which to climb. The acadmics provide the following list of suicide warning signs:
Loss of a parent, close relative, friend, other significant person or pet.
Loss of self-esteem
Loss of a job
Loss of physical health
Loss of achievement
Rejection by peers, family, authority figures or other significant persons
Changes in sleeping and eating patterns
Noticeable loss or gain of weight
Neglect of personal appearance
Abrupt change in personality and behavior (Unusual withdrawal, aggression or moodiness).
Increase in alcohol and/or drug use
Rebellion and hostility
Withdrawing from friends and activities
Appearing sad most of the time
Sudden drop in school performance
Some verbal signs are direct, others are vague or coded.
"I'm going to kill myself."
"What would you think of someone who committed suicide?"
Previous suicide attempts
Giving away special possessions
Vague complaints about health
Unusual calmness after a loss or period of depression
Suicidal notes, poems, journal or diary entries