I can assure Gino that there do indeed exist places with no sign codes whatsoever. There are plenty of them around where we are. Codes or not, you still have to hang signs right and make them right.
Since we can't see the structure you are proposing to hang the sign from, I cannot comment on that. But for a free swinging sign of that size I can comment. The best material of what's available is probably Lusterboard. The weight of the plywood does help with the swinging in the wind. You definitely want to get the edge cap and silicone it onto the sign when you finish. It's a little tricky when you have wrapped the sign with printed vinyl to the edge, as it's easy to push the vinyl off the board when you fit the edging. If you're shopping at N. Glantz they have the hanger you will need to use. https://www.nglantz.com/2231912/Product/Glantz_Preferred_Supplier_YMPH1S
Here's a picture of a sign we put up in 2009 using Lusterboard and those hangers. It's still up today, and the board is still solid with no rot. Your sign won't last as long because of the digital print, but the board and hanger concept is solid.
Since we can't see the structure you are proposing to hang the sign from, I cannot comment on that. But for a free swinging sign of that size I can comment. The best material of what's available is probably Lusterboard. The weight of the plywood does help with the swinging in the wind. You definitely want to get the edge cap and silicone it onto the sign when you finish. It's a little tricky when you have wrapped the sign with printed vinyl to the edge, as it's easy to push the vinyl off the board when you fit the edging. If you're shopping at N. Glantz they have the hanger you will need to use. https://www.nglantz.com/2231912/Product/Glantz_Preferred_Supplier_YMPH1S
Here's a picture of a sign we put up in 2009 using Lusterboard and those hangers. It's still up today, and the board is still solid with no rot. Your sign won't last as long because of the digital print, but the board and hanger concept is solid.