Unfortunately they seem to filter special characters on input, that is, when you apply for your plate.
But don't despair! Depending on how crappy the cam's firmware is, NULL might just do the trick.
Or it might do the opposite: https://www.wired.com/story/null-license-plate-landed-one-ha...
Or it might do the opposite: https://www.wired.com/story/null-license-plate-landed-one-ha...