Basic Movement/Command
Alot of this stuff is pretty obvious, but it's necessary all the same. I'll get into more complicated strategy theory in the more specific sections. This is where the most important commands are explained, however.
Unit Leader - Commanding
The man with the pistol, the one who's in the crosshairs of the gun, is the group leader. When it is necessary to give orders, the leader will back into a corner, and the rest of the group will stand in front of him to cover him while he gives his instructions. That way everyone's safe, and the leader can still give important instructions.
The idea is that hopefully the leader won't have to do this often. It's just when detailed instructions are needed. If the leader sends a message that says: "Command Support" then you know to cover him/her so they can talk. One thing too, it's likely that if we do this, we'll all have partners so that the commander can address each pair and therefore we can have multiple groups covering each other and advancing.
The message that signals to support the commander is "Command Support"
Entering Open Spaces/Turning Dangerous Corners
When you're about to enter a position where you may take fire from the side, turn sideways so you're facing the wall, then everyone can move sideways into the open, so they'll be facing the right direction when they come into contact with the enemy.
When the group is moving into the open, they need to move quickly and not stop, so as not to be shot. They need to be spread out somewhat, so that one gunner can't take all of them out. The teammates must always cover each other.
There is no command for this, soldiers do this at their own discretion.
Sniper Support
It's tough to see exactly what's happening in the pic. Basically though, this is the tactic: If the commander gives instructions to use a sniper, then the team will support the sniper. The sniper will take the lead and they'll escort him to wherever he wants to snipe from, if necessary. Usually the sniper will simply be ordered to go out on his own. Basically when the order is given for Sniper Support, the sniper can take any perch he wishes (in the picture, it's an upstairs window) and the rest of the team is supposed to cover his back so he doesn't have to worry about getting shot from behind. Remember too that the entire team probably won't cover the sniper, just those who are told to.
The message that signals to escort a sniper to his perch is "Sniper Support"
Demolition Support
Sometimes it's necessary to get a frag in a tough position, or set some c4. Both of these things take time to do well, and in most cases, a demolitionist doesn't have time. But this way, he can. If the leader tells the group's demolitionist (hopefully the group will have one) to accomplish a task, the group is to watch his back. It's hard for someone who's setting c4 to watch his own back, or worse to engage enemies, so the teammates must watch every angle.
The message that signals to escort a demolitionist is "Demolition Support."
--Griff