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Explanation: Road signs in the shape of a circle give orders. Those with a red circle are mostly prohibitive. The 'stop' sign is octagonal to give it greater prominence. Signs giving orders must always be obeyed.
Category: Road and traffic signs
References: ?The Official DVSA Guide to Riding: Section 7, Highway Code: Page 106, Know Your Traffic Signs: Page 9, Know Your Traffic Signs: Page 16
