Symbols on Airbus ASI above are:
Red Band is high speed protection region with lower end being Vmo/Mmo.
Green equals sign (left of red band) indicates area where overspeed protection occurs. When it is activated, the pitch trim is frozen. Positive spiral static stability is introduced to 0° bank angle (instead of 33° in normal law), so that with the sidestick released, the aircraft always returns to a bank angle of 0°. The bank angle limit is reduced from 67° to 45°. As the speed increases above VMO/MMO, the sidestick nose-down authority is progressively reduced, and a permanent nose-up order is applied to aid recovery to normal flight conditions. The High Speed Protection is deactivated when the aircraft speed decreases below VMO/MMO, where the usual normal control laws are recovered. The autopilot disconnects when high speed protection goes active.
Magenta triangle indicates managed speed target.
Amber line indicates present speed(also indicated by green mach readout at bottom left) and arrow is speed trend for next 10 secs.
Green Dot (Engine-out operating speed in clean configuration)
This green dot appears when the aircraft is flying in the clean configuration. It shows the speed corresponding to the best lift-to-drag ratio.
Indented amber box on top of black and amber striped tape is called Vls. Vls is the lowest selectable speed that autothrust will allow you to fly.
The top of a black and amber strip along the speed scale indicates the alpha protection speed. It represents the speed corresponding to the angle of attack at which alpha protection becomes active. Alpha protection is not unlike over speed regime where autotrim freezes, pitch attitude is maintained at alpha max and full power (TOGA) is applied.
Hope this helps,