Originally, when a student responds, my inclination is to respond back. But, sometimes, more than one student responds at once. And, if multiple students respond orally, it can be difficult to make sense of who to respond to first. On top of that, it just makes the classroom noisy. So, these are a few signals, which if utilized, will minimize the amount of noise that occurs in the classroom.
In the current classroom that I student teach in, Mr. Agajan uses a signal for "I agree," "I disagree," "I'm confused," and "speak up." "I agree" is simply signaled by giving a thumbs up with both one's left and right hands. For example, I will show a student's work under the docucam (such as math homework completed in a math workbook). For each answer that is covered, it is asked whether the class agrees, disagrees, or is confused. So, instead of everyone yelling out their response, they may give a thumbs up.
This is how "I disagree" is signaled. The palm of each one's left and right hand are facing towards the ground. They are at about chest level. One of the hands is slightly higher than the other. They are about one hand's length away from each other. While the left hand and nothing else repeatedly swings from left to right, the right hand and nothing else simultaneously and repeatedly swings from right to left. If it helps you understand it better, it looks similar to repeatedly doing the alternate possession signal as a referee would do. In any case, again, while going over the homework, if one student got a different answer than another student, then the student with a different answer would use this signal. Then, the disagreeing student would be addressed in order to determine what it is that that student disagrees with.
This is how "I'm confused" is signaled. Basically, a student just swipes his/her hand back and forth above their head with their palm facing downward.
Finally, for "speak up," a student simply points their ear at the speaker, puts their hand behind their ear, and bends the rim of their ear forward. So, say that a student is giving a presentation or a speech. Then, instead of merely raising one's hand, yelling speak up, or waiting until the presentation/speech is over to say that the speaker was too soft, this "speak up" signal can be used.
So yea, signals are a lot more diverse than a mere raise of the hand. That is, a lot more meaning can be conveyed than simply "I have something to say" as raising your hand simply implies.