Why is the letter "X" associated to pornography?

A few days ago, Elon Musk announced the renaming of Twitter to “X” as a part of his grand transformation and rebranding of the platform. Of the many reactions to the change, one of the most common comments was that the new logo was resemblant to that of a porn website. Although there was nothing necessarily pornographic about the singular white mathematical X placed on a black background, it was quite interesting to note that the natural reaction of the public to the letter in any context is an association with pornographic content. This observation raised the question, why is it that we associate the letter X so closely with erotica and where exactly did this begin ? 

The original meaning of "X"

In the present day , it’s quite easy to make the connection as there are numerous amounts of porn websites that exist that cite the letter X including  XVideos , XHamster , XNXX , TXXX , Xbabe , XXXbunker and the list can go on and on, however,  one of the original uses of the letter was the complete opposite, as it was once considered the holiest alphabetic symbols. During battle, The Roman emperor Constantine l marched with armies under the banner of an X , which latin scribes used as a shorthand for Christ for centuries. This originated from the fact that the character X was equivalent to the greek letter chi , which combined with the letter rho represented the first two letters of the greek word Χριστός which means Christos. Chi being X and ro being ρ made Χρ into a greek abbreviation for Christos which became popular throughout roman archaeology. This is also how we get to use the word Xmas as short for Christmas. However , somewhere along the centuries the letter took on a darker meaning.

What has the "X" have to to with porn?

According to Mel Magazine, the fault of the X’s fall from grace is to be blamed on Hollywood. The letter’s association with the adult industry can be traced back to a decision of the Motion Picture Association in America in 1968 on their audience-advisory ratings for movies. They used the classification “R” for restricted while using “X” for extreme. Following this, during 1970’s , porn marketing companies adopted this use of X to differentiate mainstream films from erotic content and posters , originally classifying it as “X” being hot and “XXX” super naughty. 

Throughout the decades , this was widely used by the porn industry until 2011 when it became even more official when the Internet Corporation for Assigned Names and Numbers assigned the top level internet domain “.xxx'' for release, as a way to give the porn industry its own playground separate and apart from the .coms and .orgs. Today within the porn industry, many websites and PR porn agencies are slowly shying away from the use of the letter as the xxx branding represents a very male-focused version of porn that doesn’t always resonate with a modern progressive audience. Nonetheless, decades of the porn industry’s usage of it has embedded in us a natural association to the symbol with adult content. 

Why is Elon Musk obsessed with the "X"

However , Elon Musk’s obsession with X seems to have little to do with the pornographic history of the letter. It did not start with the rebranding of twitter but dates much further back to when he started a finance company X.com in 1999,  which eventually merged with Paypal and lost its name. He eventually got fired from the company , but bought the domain name back from PayPal stating that it was of great sentimental value to him. Since then, the letter has been a big part of his life, even naming one of his children X Æ A-XII and calling his Space Exploration Technologies SpaceX . This time around Musk claims the name is due to turning the platform into an everything app which includes payments streaming video and e-commerce, and only time will tell if this is what will be its fate.