I remember going to the post office on the day new stamps were issued. There would be a queue at the philatelic counter and one had to be early if you wanted stamp blocks with traffic lights. Traffic lights in stamps are the coloured dots on stamp sheet margins printed with offset litho or photogravure methods, used by the printers to check colour accuracy. I had read in some magazine the collecting traffic light issues was a big deal. And so I would diligently go to the post office early and ask for stamps with traffic lights.