Many of you touched on a lot of my instinctive feelings but Berthier and 7eat51 caught several points well. As I said, I think this will just be a rough idea until we get the game and play. Until then we "don't know what we don't know". Some of my thoughts though...

I don't think hidden signals should be allowed or you might as well let people talk. Signals should be potentially visible to all even if they may not know them.

I think it should be presented in a model similar to the game: Basic Signals, Advanced Signals and Optional.

I would suggest this is all done as a PDF for anyone to access as it will develop as a community effort from here, basically putting this all in the Public Domain clearly up front. If someone wants to develop a nice, fancy printed version for sale then it should just recognize the IP and efforts of the SoG Anchorage community, and maybe guilt them into kicking back some funds to support here. But that's all getting ahead of ourselves.

Multiple dictionaries / signal books would be a great idea and allow player teams to pick their dictionary secretly before play and keep things difficult for the opponent go guess.

Basic Signals
* One set of signal cards used by all but a separate "dictionary" for each fleet (min of two for British & French to start obviously but maybe 5+ to allow more unknown variety).
* Most signal cards will appear on the dictionary but there could be 2-5 "undefined" cards in the set which the team can use to develop some custom orders before play.
* Signals are placed out on the table next to the Log of the ship giving the signal and are visible to all players
* Players can change signals at will.

Advanced Signals
* Players can only change signals in the shooting phase when they're ship performs its shooting. I think this will make signals much more interesting than doing it at the beginning of a new Turn.
* Signals are kept hidden unless someone tries and succeeds at viewing.
* Flags can only be attempted to be read within a range, such as 2x ruler length. This will force fleets to stay relatively close to communicate.
* Smoke can obstruct flags. We will have to see how Line of Sight and smoke are handled in the game but my gut feeling is if LoS can be established for shooting purposes then you can see signals. This will keep things simple since you can piggy back on the official smoke rule. Otherwise maybe something like this: "If there's smoke blocking your LoS you cannot attempt to read signals beyond close range. At close range draw a Damage Chit and if it's Even you can read, if it's Odd you can't. You can always read at Musket Range."

Optional
* Changing signals is an Action? Will really need to wait for the rules about this one.