could be wrong, but thought I had seen them without the additional marks - and it may well be the case that the lack of same might indicate a second.
The word originally referred to a drink made with water or "small beer" (a weak beer), lemon or lime juice, and rum, which British Vice Admiral Edward Vernon introduced into the Royal Navy on 21 August 1740. Vernon wore a coat of grogram cloth and was nicknamed Old Grogram or Old Grog. However, Merriam Webster's Collegiate Dictionary, which agrees with this story of the word's origin, states that the word "grog" was first used in this sense in 1770, though other sources cite 1749. The citrus juice was added to prevent spoilage, then it was also found to prevent scurvy, two reasons to continue the practice.https://en.wikipedia.org/wiki/Grog