The Brass Horn Cipher

Arrowyy found a string of crooked marks on the letter board behind his father and immediately appointed himself keeper of a mystery. Blaedy called it a secret message in the voice one reserves for very small children and very large conspiracies.

I failed to read two of the marks properly, which Arrowyy received as proof I need spectacles rather than proof that whoever arranged the board has the handwriting of a startled crab. Blaedy then proposed it might be an invitation token with missing values, and the pair began trying to spend imaginary fortunes on the privilege of guessing.

Arrowyy copied it down for future inquiry. I suppose this is how a series of clues begins: one brass horn, one mug, and three people refusing to leave well enough alone.