Sometimes called the “Celtic Tree Alphabet,” Ogham (pronounced, roughly, Oh-um) is made up of straight lines intersecting a staff at various angles. Atlas Obscura has posted an informative article about this unique writing system:
There are about 400 known Ogham stones in the world—360 in Ireland, and the rest scattered between Wales, the Isle of Mann, and Scotland. Most are monuments or border markers, engraved with the evocative names and genealogies of their owners—”Belonging to the Three Sons of the Bald One,” or “He Who Was Born Of The Raven.” More are almost certainly lurking—hidden stones can (and do) pop up occasionally, built into churches, unearthed at construction sites, or hiding out disguised as decorative stonework.
There’s a blink-and-you’ll-miss-it detail in Children of Pride in which an antagonist writes a line of Ogham script as part of a spell. But there was no way (or reason) to indicate that this was what was happening. I’ll leave it to my readers to see if they can track down the scene. 😉