Agree on the signwriter but maybe they have a policy of telling the customer that they will produce what is specified and the onus is on them to present it correctly in the first place.
Could the sign have been ordered through the internet? If so, if the spelling is incorrect and the order is automatically made then no signwriter would be needed.
There are several companies on the interweb that will make signs. So maybe not the signwriter, but whoever made the order.