Paddle shaft locators or Grip indexers are added to paddle shafts to provide feedback to the paddler as to the angle of the paddle relative to your hands without looking at the blade or feeling it in the water.
 
The locator is fixed to the paddle shaft using tape (e.g. electrical tape) or glue (e.g. contact adhesive) to the paddle shaft in a position where your fingers will grip the shaft. The locator is often covered with heat shrink to secure it further and make it more comfortable to grip.
 
These locators may index only one side (your locked hand, typically the right hand) or both sides.