There are also signs that appear as a huge red X symbol. Normally, when this is applied to an enemy, the general message getting across is that you should NOT attack these enemies. For example, the Ahriman in the first third of Darkhold. It can also be used in the middle of a battle where there's a point where the attacks need to stop, such as when a boss turns invincible or when attacking a boss at a certain time could end up having very negative consequences.

There are also signs useful for those players who want to optimize the speed of their targeting, such as healers in large raids (which will become especially necessary once Crystal Tower comes out). These use the symbols of a blue X, O, Square, and Triangle. These particular symbols have no exclusive purpose like the others, but can be assigned in much the same way. It's largely up to your team leader or the user of such symbols to explain what they're being used for.