A friend of mine travelled recently on a heritage railway that has an AOCL.
As his train approached the crossing it came to a stand, apparently as the white marker light was not operating. The guard got down and walked to the crossing carrying two red flags, which he used to stop the road traffic. He then waved one of the red flags at the train, which proceeded slowly over the crossing.
Not knowing the rule-book of the railway in question, but the use of a red flag to authorise a movement intrigues me. Might it have been a 'local arrangement'? Are there other situations where a red flag would be used to authorise 'proceed'?