Jean-Guillaume Olette-Pelletier, an Egyptologist and cryptologist from the Catholic University of Paris, claims to have discovered seven previously undocumented messages carved into the 13th-century BCE Luxor Obelisk. Altogether, the inscriptions were intended to establish Pharaoh Ramses II’s divine authority in the eyes of the ancient Egyptian elite.

What's a cryptologist anyway? Studies crypts or cryptography?

Some (perhaps all) of the new messages were hidden in the hieroglyphs themselves, a technique known as “crypto-hieroglyphs” used by the ancient Egyptian elite that today only six Egyptologists in the world are able to interpret, according to La Brújula Verde.

So looks like Gizmodo is sourcing this from The Green Compass, which looks like a sensationalist news from their homepage headlines. Well, let's hope Mr Olette-Pelletier publishes his paper soon.

Additionally, the messages in question can only be seen from a specific angle. In particular, when the obelisk stood at the entrance of Egypt’s Luxor Temple, one of the messages would have been visible to vessels sailing on the Nile

It's a tall structure (based on the people in the photos), stood by the Nile (presumably far from the yearly-flooding banks), with an inscription near the top that is "secret" due to the addition of one little picture of a table below the god. Did the elite have super-eyesight? I don't recall any articles mentioning telescopes. Or was this a, "You glanced at it even if you didn't see it, so it's true" thing, like an Apple end-user agreement?

The secret message is "PUT ME BACK IN EGYPT YOU THIEVING SCUM!"