These stickers were released in 1977. I have a copy of the add from then. The legit ones go for about $50 each but there are some reproduced ones for $3.99. The reproduced ones are smaller in size and have 'McJet' written on the reverse on bright white. The originals are brown or off white backing. The reproduction's backing is also not diecut like the sticker but approximately square.
Hope this helps. I am after the Canterbury one (original) if you have one spare.