As I was writing my reply, I realized that my whole argumentation is based on the following interpretation of the rules: "letters in LOS markers are there to support the rules, not to create exceptions", and if that's not true and letters may cause exceptions - to the rules and board art - well, there's no point on keep going with this discussion.
Therefore, I would be nice if we had an official confirmation or clarification.
Since I had my reply already written (and posted), I move it on the spoiler below.