Because it resembles the cross.
The New York Sun reports.
The letter “X” soon may be banned in Saudi Arabia because it resembles the mother of all banned religious symbols in the oil kingdom: the cross.
The new development came with the issuing of another mind-bending fatwa, or religious edict, by the infamous Commission for the Promotion of Virtue and Prevention of Vice — the group of senior Islamic clergy that reigns supreme on all legal, civil, and governance matters in the kingdom of Saudi Arabia.
The commission’s damning of the letter “X” came in response to a Ministry of Trade query about whether it should grant trademark protection to a Saudi businessman for a new service carrying the English name “Explorer.”..