what shape is the standard stop sign according to the highway code
Stop sign 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.[4][5] Larger signs of 900 mm (35 in) with 300 mm (12 in) legend and 25 mm (⅞ in) border are used on multilane expressways. Regulatory provisions exist for extra-large 1,200 mm (47 in) signs with 400 mm (16 in) legend and 30 mm (1 1⁄4 in) border for use where sign visibility or reaction distance are limited, and the smallest permissible stop sign size for general usage is 600 mm (24 in) with a 200 mm (7.9 in) legend and 15 mm (⅝ in) border.[6] The metric units specified in the US regulatory manuals are rounded approximations of US customary units, not exact conversions.[5][7] The field, legend, and border are all retroreflective. In the Vienna Convention on Road Signs and Signals of the UN, the instruction on the sign to stop is specified to be either in English as stop or written in the local language. Some countries use both. The sign's distinctive design was developed and first used in the U.S., and later adopted by other countries and by the U.N. Despite this, the US is not a signatory to this UN Convention.
Warning sign These signs are used to warn of level crossings ahead. In most countries, a red triangle warning sign is used, with various pictograms for unguarded crossings, crossings with manual gates, and automatic level crossings. In most of Europe, an old-style gate is used for a crossing with gates, and a steam locomotive for a crossing without gates. Germany uses an electric train. Similar pictograms are also used in Ireland, albeit on an amber diamond sign. In the United States the warning of all types of railway crossings is made using a circular yellow sign. The actual crossing is also marked with crossed "railroad crossing" crossbuck signs (stop, look, listen) and possibly lights, bells, and barriers.