In the Middle Ages, most people could not read or write. When it comes to signing documents, people who can't write usually put an "X" mark. Of course, "X" is not a signature. In order to increase a sense of commitment, it is customary to kiss the "X" after writing it.

In the Middle Ages, most people were less educated. When signing documents, people in China usually press their fingerprints. If westerners don't know how to write their names, they usually write an "X". Of course, the "X" itself cannot be used as a signature. In order to add personal information, they usually kiss "X".

Kissing "X" is a "performance method", a ritual act that binds both parties, just as legal documents bind us today. This behavior, witnessed by the person who wrote the text, represents a moral guarantee for the authenticity of the written content and an oath to fulfill any obligations stipulated in the document.

Kissing "X" is an unwritten law, just as legal documents are binding on us now. This shows that the signer guarantees the authenticity and validity of what he wrote, and is brave enough to be responsible for what he wrote.

Over the years, "X" and "kiss" have become interchangeable. Today, people who can read and write may still add one or more "X" marks to their letters, and perhaps add a few "O" s to express their hugs.

Many years have passed, and "X" has become the symbol equivalent to a kiss. When people write letters, they will add "X" for kissing and "O" for hugging.

The Oxford English Dictionary points out that "X is used to represent kissing, especially." . In a letter of subscription. ”。 There is no general consensus on the origin of "O" as a hug. O may be related to the shape formed when two hands cross and hug, forming an O-shape. X may also refer to the contraction of lips when kissing.

The Oxford English Dictionary describes X as "used to express a kiss, especially at the signature of a letter". However, there is no universal understanding of the origin of O as the meaning of hug. The letter o may be related to the shape of o when hands overlap when hugging. The letter X may also be related to the shape of the pouting lips when kissing.