Or word mark, word-mark. How did I miss this for so long. I just came across it in Wikipedia, checked it out in OED and found that it’s been with us for over a century.
word mark, n.
1. A (real or invented) word used as a trade mark; a trade mark in the form of a word (as opposed to a design, a colour, etc.). Also: a word used in a distinctive style or font as the symbol of a company, institution, etc.
1902 Encycl. Brit. XXXIII. 387/1 The registration of ‘word marks’ was first provided for by the Trade Marks Act, 1883. In that statute, however, clause (d) read ‘a fancy word or words not in common use’.
1920 Yale Law Jrnl. 29 306 There are different opinions as to the essence of the word-mark.
Incidentally here’s something that interested me in the 1976 cite for the word.
1976 Century of Trade Marks (Patent Office) i. 1/2 These were early instances of word marks, though usually in conventional form—for example, CATIM (Cati manu: from the hand of Cato), and OFALBIN (officina Albini: the workshop of Albinus)—whereas earlier marks had been almost invariably devices or ideographic symbols.
I know we’ve discussed pre-20th century acronyms, or rather the lack of them, several times on the board. Would these qualify at all?