I downloaded a pretty cool sword bookmark from @MatthewForde, but it hit the cover of my book before or after a certain point.  It's probably fine for softcover, but for hardcover it only really worked right in the middle of a sufficiently thick book.

I wanted one that stuck out of the side to easily see progress, but only stuck out to one way so it could be reversed after a certain point to avoid it colliding with the cover.

I was honestly a little surprised that no one had made it before, so I got to work in Tinkercad.

Circle for style, triangle for simplicity, and square for surface area.
Feel free to add a cutout for initials, a logo, or something from your favorite book.  I have added a couple extras from some popular franchises, as well as one from one of my favorite books.