How do you find out if someone is under the influence of an illegal stimulant through observation?

People on stimulants tend to have dilated pupils, agitated behavior, rapid or excessive speech (often called "verbal diarrhea"), hypervigilance (looking around in a circumspect manner), anxiety, aggression, and/or paranoid symptoms. They may also have pallor due to vasoconstriction shunting blood away from the skin. Checking for vital signs, you will often find increased blood pressure and pulse, due to adrenergic effects of stimulants on the nervous system.