There abound many theories as to the origin of the XOXO meaning kisses and hugs but one thing is for sure, it abounded in jewelry from the 1970s onward. In fact this trend was so strong that it is still with us today.
Yes, for many a year an X was a signature and often sealed with a kiss to demonstrate sincerity. There seem to be many versions of why the X signified a kiss. As for the O, one interesting theory is that early immigrants to the United States would sign their name with an X because they did not know how to write. Jewish immigrants, because an X was too much like a cross, signed with an O.
I’m not sure how that relates to the O being a hug though.
From what I could find, the earliest mention of X and O together was a letter dated 1960, in a letter to Santa. The X and O together began to be seen regularly in about 1972 in personal ads.
What this can tell us though is important. Since so much jewelry was done in an X and O pattern, it is best to assume that it is from the 1970s and later. It is a safe assumption.
Let me just say that there may be exceptions, as there always is to any rule, but as a general rule of thumb this is a good one to keep in mind.