What geometric shape is a stop sign used in English-speaking and most European countries?

A stop sign is a traffic sign to notify drivers that they must make sure no cars are coming and stop before proceeding. In geometry, an octagon is an eight-sided polygon or 8-gon. In most English-speaking and European countries, a stop sign is a red octagon with the inscription "STOP" in white.

The United Kingdom and New Zealand stop signs are 750, 900 or 1200 mm, according to sign location and traffic speeds. In the United States, stop signs have a size of 750 mm across opposite flats of the red octagon, with a 20 mm white border. The white uppercase letters in small caps forming the stop legend are 250 mm tall.