I think the "single letter" part is important here. AFAIK trademarks can't be too simple and generic. Sort of like how Intel couldn't trademark 286/386/486, so instead of 586 we got Pentium.
Intel lost their trademark battle because they didn't attempt to register the trademark until the 486 - more than a decade after the numbers were in common use by other chip manufactures.
It has nothing to do with whether the mark is simple.
It does say "Standard Character Claim: No" which (as best I can tell from [1]) means it is the particular form of that letter[2], not the letter itself, which is trademarked.
I thought that Peugeot had a trademark on car models of the form X0Y (where X and Y were single digits), resulting in the Porsche 901 being renamed to the 911 that we now know.
3M, Scotch, Crate & Barrel, Lufthansa and Jeep all have legitimate trademarked word marks that consist of nothing more than their name written in Helvetica.
The typographical and design treatment of the word can have separate trademark protection.
That can be true whether or not a design mark is registered.
If you started a car company called ‘Beep’ and write its name in olive green Helvetica Black, Jeep might struggle to make a case about your name’s similarity to their word mark (beep is a different word and rhyming is not a crime), but they for sure could take you to court for stealing their trade dress.
Not in the word mark registration, sure. But registration is not the whole of trademark law is it?
‘Word mark’ is also just a term of art in graphic design referring to a logo consisting of just text - another word for logotype. Should I have said logotype instead?
