I've seen a few articles on this now. They keep calling it a "secret" message and "hieroglyphic cryptography," but then talk about how sufficiently literate people are supposed to understand it, and the content is along the lines of "The god-king cannot be dethroned" and "Make offerings to the gods." Nothing about this sounds like it was intended to be kept secret or confidential from anyone.

This seems more like fancy typesetting than cryptography, combined with an awareness that the writing at the top of a big tall obelisk will only be readable from a distance.