That is not how Trademarks work. It isn't "We used it first, so no one else can". If you are in an unrelated industry, selling unrelated products you can use any name that might be trademarked in another industry/product space.
> For instance, the name "MY GIRL" is a registered trademark owned by Enertec Enterprises for a line of dolls and accessories. However, there is a second trademark registration for the same name "MY GIRL" that is owned by Acushnet Company for a line of golf putters. The reason that these two different companies could register a trademark for the exact same name is that they operate in totally unrelated industries, and offer totally unrelated products. One company sells dolls, whereas the other company sells golf equipment.
A trademark can be registered for one or more classes of goods/services [1]. The APPLE M1 mark [2], for example, is registered across multiple US classes (21, 23, 26, 36, and 38). I did not immediately find a registration for US M2-based marks by either BMW or Apple. Maybe that's coming soon. Or I didn't input the right incantation into TESS [3].
And while there is a concept of a "famous trademark" that can provide general protection across all industries against trademark dilution, it is extremely unlikely something as generic as a letter and a number would receive such protection.
> For instance, the name "MY GIRL" is a registered trademark owned by Enertec Enterprises for a line of dolls and accessories. However, there is a second trademark registration for the same name "MY GIRL" that is owned by Acushnet Company for a line of golf putters. The reason that these two different companies could register a trademark for the exact same name is that they operate in totally unrelated industries, and offer totally unrelated products. One company sells dolls, whereas the other company sells golf equipment.
https://secureyourtrademark.com/can-you-trademark/trademark-...
No one is going to confuse a Mac Book for a luxury car, or vice-versa.