I wondered if this was a reflection of the laissez faire attitude to otherwise-law-abiding casual speeding nowadays. I've seen a surprising number of vans and small coaches this year wearing rear door stickers that say "This vehicle is limited to 70mph", with a big 70 symbol.
Did they increase the speed limit when I wasn't watching? Or is it supposed to be a subtle "don't misjudge your skill level and try to overtake" warning?