Just a quick question to anybody who might know, but recently there has been a fairly large white square painted on the up platform at Chorleywood station. It has a thick black outline and it is painted in the sort of paint which suggests it is going to be there for quite a few years before it fades. Does anybody know it's purpose? I presume it is some kind of marker for the new Met line trains, much like other markers painted on Underground platforms, but this is so much bigger and brighter it really stands out. It is also quite a way away from where any driving cab would be on the platform of the station other than the two or three car Class 165 Chiltern services which call there en route to Marylebone, so I cannot figure out its specific purpose. So, what is it for and is it duplicated anywhere else on the Underground?