There was a time when affectionate letters were signed with XOXO meaning "hugs and kisses". Now, communication comes in many forms and the written word is just one of them. Phone calls, text messages, emails, digital pictures, videos are all used to communicate, leaving the traditional letter in the dust.
As a kid, I remember signing my name to family with a XOXO. It was a way to send extra special "love" when I wasn't there in person.
There is some discrepancy as to which stands for the kiss and which stands for the hug. Here is what I think.
The "O" represents arms wrapped around someone and therefore the hug.
The "X" represents the kiss. Years ago, people who could not write their names, signed documents with an "X". When someone who couldn't write, signed their name with an X, their action was witnessed by others who saw them take their sworn oath. This was then kissed as a sign of honesty.
Some people associate the X with the symbol of the Cross or taking the place of Christ.
"X" as a kiss in literature can be traced back to 1901.
Another sentiment that was written on letters was "S.W.A.K" meaning- Sealed With A Kiss or Sent with a Kiss, to express longing or missing for the recipient.