Harpspeak

Harpspeak was a form of sign language employed by the Harpers in the years during, and preceding the mid–14 century DR.

Description
Each expression or gesture made by the user―such as a suble wink or a frown―built upon that which preceded it. Two expressions made together could have one meaning, while those two made in reverse meant something else entirely. These signals difficult to interpret by Harpers proficient with the language, and entirely undecipherable by anyone else.

Harpspeak was said to be similar to drow sign language, though distinct enough that drow themselves could not interpret its meaning.

Usage
Harpspeak was not rarely if ever used by novice Harpers, but rather senior members and the Master Harpers themselves. Even of them, only a select select few actually mastered its usage. The coded language was never taught to non-members.

Rumors & Legends
It was said that learning to sign Harpspeak could be somethin of a quest unto itself for novice Harpers to undertake. It was so difficult to master, that misinterpretations during its use were quite common, often leading to confounding or even disastrous results.