Currently there's not really many options when a group of players are on a stealth mission and don't want to use VON as the enemy might hear them. IRL, they might tap on the other players shoulder and give a hand signal or mouth a few words but this isn't possible in Arma.
So what I suggest is a way to bring up a scroll-list of signals, i.e. "Moving Left", "Pulling Back", "Understood", etc and then when one of these is selected, the player targeted/directly in front of the player sees this message quite clearly on their screen. This avoids the need to have complicated keybinds to remember for different hand signals that the other players might not even recognise (and to even see the signal the first player would first need a way to get their attention and to turn and face them), without allowing for unrealistically detailed messages to be given over text chat.
The same method could be using for house-clearance, etc to simulate a hand signal or head nod.
A more realistic/hard-core alternative would be when selecting one of these messages, it could automatically cause the receiving player to turn to face the sending player and then use hand signals rather than text messages, which would simulate the person's attention being first obtained by a tap on the shoulder or a quiet whistle, causing them to turn to the person wishing to communicate with them.