Your personal logo, in my opinion, is much classier and appealing.

Combine them

Personal logo for your profile. Codex logo for your book.

Consensus seems to be leaning strongly toward personal logo, so I've changed it back for now. Thanks everyone for the feedback.

Utilizing a logo is an aspect of branding, which is a form of promotion. So the question appears to be:

Should I promote my book or myself on this forum?

That depends on what your goals are and whatever strategy you may have developed for achieving those goals. I would guess that you're at least mostly interested in promoting your book and haven't really put much thought into a plan for doing that, or perhaps even a firm end-goal. Of course, a common approach is to use a personal brand to promote a book, in which case you might want to reconsider branding the book itself, with a logo and whatever else.

Note that an essential quality of branding is that it should be as meaningful as possible to whomever you're trying to promote it to. I find the book branding to be meaningless, if not plain false. The "book of questions" is really a book of your views or a 'book of answers'.

Your personal logo gives me the impression that you value nature.

I'm not trying to promote anything here, I'm just wondering if using an image associated with my philosophy might be more appropriate for my account on a philosophy forum than an image that's not philosophically relevant at all, just what I use everywhere else.

"Book of questions" is more like "book about inquiry" than "book containing a bunch of questions", BTW. I specifically changed it to that way to get away from the connotations of an earlier title that was meant to be "book about wisdom" (as wisdom is the topic of philosophy) but could be misinterpreted as "book containing wisdom" Success at inquiry is what wisdom is all about.

I'm not trying to promote anything here — Pfhorrest

Of course you are. Your personal logo, for instance, gives the impression (to me at least) that you value nature, and in effect promotes that value.

You might say that you’re not deliberately or consciously branding. If so, it’s kind of funny that you’re using a method of deliberate branding (logo design) so casually. Not to suggest that there’s anything wrong with that, other than possibly being blind to ones own motivations to some degree.

Speaking of wisdom, the maxim gnothi seauton comes to mind.

I’m a graphic designer for a living. I like logos for themselves, little graphical encapsulations of things. What are user avatars at all if not that same thing, an icon, a little graphic, to represent you? I just like to make mine rather than find them. If you want to call that “branding” when it has nothing to do with any kind of commercial activity, that’s your business.

As I said from the start, branding is a form of promotion. Promotion isn’t necessarily commercial, obviously.

What are user avatars at all if not that same thing, an icon, a little graphic, to represent you? — Pfhorrest

Ain't that the truth mate.

But what does mine say about me?

I like your logo! It looks amazing! — CraigAten

Thank you very much! Though I'm not sure how this ancient thread came to your attention. :)

what does mine say about me? — Sir2u

I don't know.

Sorry, I meant: "I don't know."

I.e. it says that you don't know; that you question.

;)

The JWST mirror bears a striking resemblance to the OP's codex logo (hexagons).