i'm sure these signs never used to give the reason.  or perhaps i've only just spotted they do.  anyway, this is ideal if you want to see the curry boys being filmed.  whatever that is.  (i think it's unrelated to the advert being filmed a few streets away).  there was also some filming trucks and food place next to the Royal Albert Hall yesterday.  no idea if it's related.  sorry for my lack of knowledge.  i do my best, but you know.  sometimes.  it's just not good enough.