You can use an underscore or if you want to have a different caption label than identification name, then you can also use .setCaptionLabel("something else");

Code Example

1. import controlP5.*;
2. ControlP5 cp5;
3.  
4. void setup() {
5.   size(700, 200);
6.   cp5 = new ControlP5(this);
7.   cp5.addSlider("awesome_slider")
8.      .setBroadcast(false)
9.      .setRange(0, 200)
10.      .setPosition(50, 50)
11.      .setSize(500, 100)
12.      .setValue(100)
13.      // .setCaptionLabel("something else")
    
14.      .setBroadcast(true)
15.      ;
16. }
17.  
18. void draw() {
19.   background(0);
20. }
21.  
22. void awesome_slider(float value) {
23.   println("an awesome slider event: " + value);
24. }