King’s Shilling
Given to recruits of the Royal Navy in the 18th century, “to take a King’s Shilling” was to enter service as a sailor or soldier. There is a legend that says recruiters would slip a coin into their victim’s drink to con them into accepting service. Glass-bottomed tankards were designed to allow the drinker to see if a coin was in the bottom before they accepted a drink.
See also: Royal Navy, tankard