Before the British currency was decimalised, there were coins still in circulation going back to the early years of the nineteenth century. The biggest of the copper coins was the penny. The Victorian penny went through several modifications: the young Queen's head became eventually an old Queen's head, and on the obverse, the seated figure of Britannia was similarly modified.
Don't go, the funny part is on its way.
The joke was to ask someone if they had ever seen a "honolulu penny". When they (you hope) said no, you showed them the pennies illustrated above, the right-hand one being the earlier version. The punch line: "See, on the left-hand penny, the trident is on her knee, in the right-hand penny, it's honolulu!"
Oh how we laughed. Remember there was no such thing as television or the internet in those days: we had to make our own entertainment.
For the first time, I realise that a by-product of a bad cold is delirium. Sorry about that.