A sign is something others, like the doctor, see, whilst a symptom is something that the patient discerns and explains. Example is the case of dilated pupils being a sign while constant sleepiness is a symptom.
Substance dependence is when someone is addicted to a something like drugs or alcohol and they are not able to control their use of the substance. He/she continues to use it, despite the fact that it may be harmful (the person may or may not be aware of the possible risk).
Uncontrollable urge could be occasioned by dependence on a substance. It will be extremely difficult for the addict to stop using the substance without external assistance, even when they want to.
The signs and symptoms of substance reliance change as indicated by the individual, the substance they are dependent on, their family history (hereditary qualities) and individual conditions.
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.