What are the early signs of glaucoma?

None: None that you would notice since it starts out with visual field loss (peripheral vision loss) that progresses slowly typically over years. The exception is acute angle closure glaucoma that presents with painful red eye and blurry vision due to acute increase in eye pressure - a medical emergency.

Several: Early glaucoma has no symptoms. Signs are what the doctor detects and include in this condition: elevated eye pressure, thin corneas, enlarged discs and changes in the field of vision.