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Rich, The size, location and type of lettering are all covered in 14 CFR 45.22 through 45.29. I see these words in 45.25(b)(1):
(1) If displayed on the vertical tail surfaces, horizontally on both surfaces, horizontally on both surfaces of a single vertical tail or on the outer surfaces of a multivertical tail. However, on aircraft on which marks at least 3 inches high may be displayed in accordance with §45.29(b)(1), the marks may be displayed vertically on the vertical tail surfaces.
I think the answer to your question if that particular N-number placement is ok is, "probably." But different inspectors may view the reg differently and have a different interpretation of the word "vertically."
14 CFR 45.23 specifies "Roman Capital Letters." Don't know what font is in the picture, but it's not Roman Capital!