If you can, design your 4 by 8 sign with some cut out portions to help eliminate the ability to catch the wind, thereby getting blown over.
Of course these cut out areas could also help to create sort of a "3-D" look to the signs.
My 4 by 8 sign on my homemade axle blew over so many times!
I finally have enough 5 gallon buckets full of concrete chained and wired to the sign to keep it under control.
I think it took about five buckets and cutting the "R" out of GRIN to keep it where I wanted it?