From my game Trap Farmer Brer Brah.

The 21 symbols of the written language used by "Eshira" - terrestrial zooid colonies amalgamated from bacterial, viral, fungal, plant, and animal components. Eshira use this language by secreting an enzyme at the top of their rocky, stromatolite-like structures, dissolving the material to reveal white glyphs. These glyphs are extremely shallow engravings, and material is removed much slower than it is added through metabolism. They are formed so that wind, rain, UV exposure, and/or wave action naturally weather them off in a day's time.

Each glyph represents an entire concept, question, plea, or rebuke. The glyph that appears depends on the eshira's environmental conditions and treatment. Intelligent creatures on Planet Fyromr read these glyphs to determine whether the fishing is good, what the weather will be like, whether their aquacultures and aquatic farms are healthy, and so on.

An eshira only etches one glyph at a time, so these symbols are only ever meant to appear one at a time. All the eshira in a particular place tend to produce the same glyph at low tide.