Yes, this is the underside of my toilet tank lid... You will note the backwards "S" and also the blot-out, which I believe is a 4 on top of a 3. This, along with the month and day, dates this to March 27, 1984 - which is just about right considering when the house was finished. We have three toilets in the house; each has different dates, but all three have the backwards S ! And you thought silly human errors like this were a thing of the past...