I want to know what's the sign of having meth mouth?

Not exact...: Not an exact diagnosis, but usually characterized in quickly appearing cavities (very noticeable) in an adult. Other factors are irritability, very irregular sleep cycles. You will find plenty of photos if you google this.

Meth Mouth: Generally a rapid onset of tooth decay, usually due to lifestyle change that accompanies the addiction, lack of sleep and oral hygiene, increased sugar intake, less saliva. Other signs can be irritability, inability to stay focused, changes in skin tone and increased blemishes to name a few.

Total tooth deacy: The extensive tooth decay is due to psychological and physiological changes caused in dry mouth, long periods of poor oral hygiene and after the "high phase" cravings for sweet soda drinks. Excessive grinding and clenching are a contributory factors for tooth destruction.