Shadowscript

The Obsidian Syndicate employs a unique method of cover communication during their operations, known as "Shadowscript". The Shadowscript communication involves the generation of magical symbols in the air, which are only perceivable to those wearing the rings of decoding on their right middle finger.
To employ Shadowscript, an operative forms a wisp of concentrated shadow energy from their fingertips and traces it through the air to create various symbols. Only certain ranks of the syndicate are trained to cast the communications and more ranks are given rings to understand it. You may only read the messages that have been assigned to your rings rank and below. This allows quick execution of orders and no need for hiding certain communications from other operatives as they wouldn't be able to discern it anyways.
When a Shadowscript message is scribed it can be set to last for a certain amount of time, some scribings existing for thousands of years. The message also is overlaid to keep down suspicion of lower ranks, by doing this when you cast the message anyone that can decode it will see a message but the message changes for each rank.
Mastering Shadowscript demands skill and precision; a small error in forming a symbol could distort the message and risk compromising an operation. Syndicate operatives undergo years of training to perfect the art of Shadowscripting.
There are also a few types of emergency Shadowscript capsules that are handed out to the lower ranks, these capsules can be broken open to reveal a Shadowscript message. The messages crafted for the capsules are for a few common phrases, like "Danger Ahead", "SOS", "Reinforcements needed". Depending on the urgency of the capsule messages they may also contain alerts that rocket into the sky allowing the syndicate to hone in on the location.