A sign is something other people, like a doctor, notice while a symptom is something that the patient describes. To give an example, enlarged pupils can be a sign, whilst sleepiness can be a symptom.
Dependence on a substance - the person who is addicted to a substance like alcohol or drugs loses the ability to decide when to use and when not to use such. They keep taking it, despite the fact that it might bring about mischief (the individual could conceivably know about the potential damage).
Uncontrollable urge could be occasioned by dependence on a substance. Addicts may desire to quit (give up), however experiences it very hard to do without assistance.
The clues and indicators that someone is addicted differ from one person to the other, depend on the drug, the genes of the individual and status in life.
The clues and indicators of addiction could be that:
Some people who abuse drugs or alcohol might not be technically addicted but can still suffer the effects mentioned here but do not usually suffer from withdrawal symptoms or have the same obsession to use the substance.