Interchangeable Letter sign box

[signtologist]

I am looking for a Interchange letter sign box system that I will put up on posts. Does anyone know of a company that sells the sign box.

[Mosh]

Excellart sells a knock-down kit. with and without vandal covers. You have to assemble this, so you will need tools and some know how.
Any sign up in the air on a pole should be designed by an engineer.