Letter kerning is where a V will overhang a O to close the gap so that the space looks the same as two  letter I’s. on changeable signs this can not be done, impossible. all the letters are on square panels so it is impossible to overhang a letter over another. Some people say auto kerning is that a W is wider than an E , that’s letter width and has nothing to do with kerning, we are signwriters for 50 years