I agree that all of Don's light are very unique and easily distinguishable from the majority of other lights. I do like the "unblemished" looks of the lights as well. However, a logo or some other type of Artisan's mark does not necessarily have to be out-worldly visible or if visible, detract from the beauty of the light. For example, a hand-scribed autographed piston in the PD lights. (Think, Malkoff drop-ins.) In the case of the Sapphires, it would help distinguish between the mass-produced Arc variants and the McGizmo version. (Think, PK logoed Surefires.)
The main reason to include some sort of marking is for the sake of posterity. As humans, we tend to think in the short term. Consider though, a future CPFer 10,25 or even a 100 years from now trying build an authentic McGizmo collection. Plus, it gives non-CPFers who may stumble upon a lost McGizmo some where a starting point to google.
In any case, I am sure that if Don ever decided to brand the lights in some fashion, it would be done well, elegantly and up to his high standards. My vote is for a big McG logo visible in the beam pattern.