The answer to this question—”Who owns the ‘Taco Tuesday’ trademark?”—is actually quite straightforward: it’s American fast food chain Taco John’s. According to an article in The Guardian, the fast food chain Taco Bell is currently battling “to liberate [the] trademarked phrase”.
Taco John’s Chief Marketing Officer Barry Westrum is quoted by the Guardian saying, “It’s been ours for 34 years, and we’re very proud of that… To this day, Tuesdays are our bestselling days of the week. While Taco Tuesdays may have become part of the American lexicon, that doesn’t give our competition the right to take it from us.”
This timeline is contested, however, as evidence of businesses using the term back in the 1930’s was raised by author of Taco USA Gustavo Arellano. Read more about the Taco Tuesday trademark over at the Guardian.