The rules around this issue vary depending on where in the world you are however in the UK the DSA say that your vehicle must pass MOT in which the condition of mirrors and other safety equipment is required.
They use convex mirrors to give a wider view.
So. It can be read by drivers looking in there mirrors
Called side mirrors. Drivers side mirror/passenger side mirror.
Convex mirrors used in vehicles provide a wider field of view, allowing drivers to see a larger area behind them. This helps reduce blind spots and improve overall safety by enhancing visibility of surrounding traffic. Additionally, convex mirrors make objects appear smaller and may help drivers judge distances more accurately.
Curved mirrors, such as side mirrors and rear-view mirrors in cars, help drivers by providing a wider field of view, reducing blind spots, and enabling better visibility for parking and lane changes. They allow drivers to see objects and vehicles approaching from different angles, enhancing safety on the road.
All state laws require vehicles to have rear view mirrors (the ones that mount to the interior windshield).
Convex mirrors are often used for side mirrors (if the mirror has a note saying "objects in mirror are closer than they appear," it's convex; it may be convex even without such a note).
That is so drivers in front of the emergency vehicle can read what it says in their rear view mirrors.
Convex mirrors are commonly found in stores, parking lots, and driveways as security or safety mirrors to provide a wider field of view for drivers and pedestrians. They are also used as rear-view mirrors in vehicles to reduce blind spots. Another example is in decorative or cosmetic mirrors due to their ability to make spaces appear larger.
"Convex mirrors are used to provide a wider Field_of_viewthan a flat mirror, and are often used on vehicles, especially large trucks, to minimise Blind_spot_(automobile)."http://en.wikipedia.org/wiki/Mirror
Plane mirrors provide a wider field of view compared to curved mirrors, allowing drivers to see more of their surroundings. They also do not distort the image, providing an accurate representation of objects behind the vehicle. Additionally, plane mirrors are more affordable and easier to manufacture than curved mirrors.
curved mirrors are useful to driver to see what is in the back of them or use for seeing