Last week I unearthed a mystery. Hardly a mystery of Mulder-and-Scully or Miss Marple proportions, but a mystery nonetheless.
Arriving at London's King's Cross by Tube I heard an announcement instructing me and fellow passengers that we should "alight here for the National Institute for the Blind".
I wondered whether this was the result of a clever marketing ploy by Britain's leading charity for blind and partially sighted people. Tens of thousands of passengers pass through King's Cross every day - what better way to raise awareness of the charity than to get a free name-check at the station nearest to its headquarters?
Perhaps this is the new trend in advertising. Next the tannoy at Vauxhall Station will be directing commuters to the Refugee Council, or First Great Western Trains will alert us to the fact that Oxford is the home of Oxfam.
Strange, then, that London Underground seemed to be unaware of the institute's royal patronage. Surely, I thought, the RNIB would make sure that its own publicity bears its correct name?
So then I began to wonder whether the King's Cross announcement might actually be the result of a concerted effort on the part of London Underground to improve disability access. The RNIB runs a resource centre at its Judd Street headquarters offering product demonstrations, a video library and support equipment for blind or partially sighted people to purchase. I'm told the centre is well-used. Perhaps, given their less than excellent record on disability access, London Underground is seeking to make amends.
Except that when I telephoned, the RNIB was none the wiser either, although grateful for the free promotion. It has long called for audio announcements to be made on all public transport. But as far as it was concerned, blind and partially sighted people could still be better helped to find many of London's important landmarks.
It's a real mystery. No doubt someone knows the answer. Answers on a postcard, please, before London Underground gets inundated with requests from thousands of the capital's charities.