there are four kinds of marks representing the year of manufacture, namely [] (since 1957), [|] (from 1966 to 1973), [/] (from 1974 to 1981) and [\] (from 1982 to 1986). Each mark is used for 8 years. There are at most eight of these marks, which are engraved on the left and right sides of the ZIPPO trademark (that is, there are at most four marks each). And adopt the method of decreasing year by year, leaving at least one.

since p>86, in addition to the year, the month mark has been added. On the right side of the trademark, Roman numerals indicate the year of manufacture (II stands for 86 years, III stands for 87 years, and IV stands for 88 years); The English letters on the left represent the manufacturing month (A stands for January, B stands for February, and C stands for March).