This type of construction is rarely done here in Ontario Canada, I have installed American sign shipped to me like this. Usuall hire a certifield welder to do the plug welds. But agree with the rest of the forum.
I agree on this one, then base /anchor bolts should be checked.
A lot of people will take a small sign and install a larger one without taking stoack on the engineering requirements.
Here we engineer at 30#/sq in with that kind of wind load happening once in a 100 years