The wording of the CAR on marks is difficult and convoluted, yes, but if you take the time to parse it and deconstruct it, it is clear. Marks must be on fixed surfaces, and if you don't have letters on your wings you have to put them on the side of the aircraft... Not the tail.
However, as Norm points out, what is being accepted as correct varies from region to region across the country. I don't know any RV's with lettering on the wings, and there are many locally with marks on the tail that span onto the rudder. As long as they are 6" tall and legible, you won't get any complaints.