Code Black

A Code Black was a transmission made by the $𝜇$ in the mirror universe.

In 2377, the Obsidian Order made a Code Black transmission to Intendant $𝜇$ (who was actually Iliana Ghemor posing as the deceased Intendant) when the arrived at a rendezvous with an Alliance battle fleet at Regulon. 
 * ''Given Ghemor's familiarity, the primary universe Obsidian Order might have used Code Black transmissions as well.