On a power diagram, the symbol may be used without other identification. On a composite drawing where confusion with the general circuit element symbol may result, add the identifying letters CB inside or adjacent to the square.
A set of speech bubbles in .svgz. If you have your software set the right way, the stroke won't be distorted or capped off when you resize it. Unfortunately, there is no way to change the position of the spikes. Additional bubbles are coming later.