There are many signs that show someone is depressed. People who suffer from depression may not show every symptom. The severity of the symptoms may also vary.
The National Institute of Mental Health posts a list with symptoms of depression. They include:

• Persistent sad, anxious, or "empty" mood
• Feelings of hopelessness, pessimism
• Feelings of guilt, worthlessness, helplessness
• Loss of interest or pleasure in hobbies and activities that were once enjoyed, including sex
• Decreased energy, fatigue, being "slowed down"
• Difficulty concentrating, remembering, making decisions
• Insomnia, early morning awakening, or oversleeping
• Appetite and/or weight loss or overeating and weight gain
• Thoughts of death or suicide; suicide attempts**
• Restlessness, irritability
• Persistent physical symptoms that do not respond to treatment, such as headaches, digestive disorders, and chronic pain

**If you have thoughts of suicide, or have attempted to hurt yourself, please call 911 immediately.