If we want to get into the weeds, lets take a look at the signs and see what we can come up with.
1 Sign of Recognition Allows the character to identify other members and their relative ranks. - Seems fine to me.
2 Signal Use sign language to communicate with other society members in the room. - Would be nice to see RP verbs added for CoL only members.
3 Sign of Warding +5 to DS. 1 0 Invoked 10 sec/level - Short of a base duration change, I think this is fine.
4 Sign of Striking +5 to AS. 1 0 Invoked 10 sec/level - Short of a base duration change, I think this is fine.
5 Sign of Clotting Stops all bleeding. 1 0 Invoked 10 sec/level - Redundant with Staunching. Should be removed or replaced entirely.
6 Sign of Thought Gives the same effect as rubbing a crystal amulet. 1 0 Invoked - Seems fine.
7 Sign of Defending +10 to DS. 2 0 Invoked 10 sec/level - Short of a base duration change, seems fine.
8 Sign of Smiting +10 to AS. 2 0 Invoked 10 sec/level - Short of a base duration change, seems fine.
9 Sign of Staunching Stops all bleeding. 1 0 Invoked 20 sec/level - Combine with clotting, otherwise very useful.
10 Sign of Deflection Adds +20 to Bolt DS. 3 0 Invoked 10 sec/level - Short of a base duration change, seems fine.
11 Sign of Hypnosis Calms a random target with a hidden warding check. 0 1 Invoked Variable - Would change to a system where you can charm certain creatures for a set amount of time. Would no longer be hostile unless attacked, instead attack others. Cost could vary by target type/level.
12 Sign of Swords Adds +20 to AS. 0 1 Dissipates 10 sec/level - Possible base duration change, otherwise fine.
13 Sign of Shields Adds +20 to DS. 0 1 Dissipates 10 sec/level - Possible base duration change, otherwise fine.
14 Sign of Dissipation Adds +15 to TD. 0 1 Dissipates 10 sec/level - Possible base duration change, otherwise fine.
15 Sign of Healing Fully regenerates all hit points. 0 2 Invoked - Seems fine.
16 Sign of Madness Adds +50 to AS and subtracts -50 from DS. 0 3 Dissipates 15 seconds - I'd stretch out the bonus and penalty phase and lower/eliminate the spirit cost. Add a cooldown timer with escalating costs.
17 Sign of Possession Mass calms the room with a hidden warding check. 0 4 Invoked Variable - Same as Hypnosis. Could either be combined and allow for open/focused cast, or remain room wide with same purpose.
18 Sign of Wracking Fully regenerates all mana. 0 5 Invoked - I'd up the cost to 6, but otherwise balancing this sign is tricky without significant revisions elsewhere. 6 points would mean investment in Aura enhancives in order to to use multiple times in a row, which is fine.
19 Sign of Darkness Teleports the user to a "safe point" or to the nearest Council chapter (whichever is closer). 0 6 Invoked - Lower cost and add the ability to use the sign when under duress in exchange for a -3 penalty to spirit recovery for a set amount of time.
20 Sign of Hopelessness Causes you to decay while dead. - I liked the ability to kill yourself on command. Not sure why they nerfed that.
General notes: I'd like to see base durations of CoL signs raised a bit, and a small reduction on the high end. 2 minutes off the top and added to the base would be a good start.
They could add a ton more signs, so it'd really depend on where they wanted to take the direction of the society to come up with ideas. I think messing with Spirit recovery for CoL signs as a cost is a good idea. This could be offset by doing upkeep tasks for the Council, or just paying an increasing bribe in order to bypass the busy work as a possible silver sink.
In general, I like the idea of being able to manipulate creatures to fight along side you, if briefly. It fits with the corrupting nature of the society. It'd be neat to see innate bonuses against certain creature types along with innate weaknesses. These modifiers could be modified both in the characters favor or to his detriment depending on how involved they are with the Council, providing a means of upkeep costs and potential RP hooks down the line.