The name of Elon Musk's daughter with Canadian musician Claire Elise Boucher, known professionally as "Grimes." X AE A-12 was born on May 4, 2020. Having named his financial services company x.com, his rocket ship company SpaceX and renaming Twitter to X, Musk is obviously quite fond of the 24th letter of the alphabet. The A-12 stands for Archangel 12, the 1960s reconnaissance aircraft built by Lockheed for the CIA, which was the precursor to the SR-71, "the coolest plane ever" according to Musk. See
X.com.
Uncommon to Say the Least
The AE ligature, which is technically not valid on birth certificates, is pronounced "ash" according to Musk. X AE A-Xii is the Roman numerals version (X=10; ii=2).