The whole point of the exercise was to remove all the graffiti, not just that partially covering the speed limit. I was not worried about the speed limit being obscured - I think all drivers know what the speed limit is in a school zone. What I was worried about was the message that the graffiti sends to impressionable young minds. Only doing 50% of the job is not enough!
I've left a followup comment on the RTA website as a result. Let's see if they can get it right second time around.