If it were me, I would opt for an alumalite composite sign in a sturdy wooden frame.
If that is not an option, I always used ½" exterior plywood, A/C (means good on one side)
I cut it to shape with a handle in the top and legs on the bottom.
Sand all edges and seal them with tite-bond 2 wood glue.
Two coats of Kilz primer then a coat of bulletin or lettering enamel for the background.
You could even tape off an area and paint that portion with chalkboard paint.
Paint the backs flat black latex for a nice professional look.
Make sure you seal the bottom of the sign really well.
(I've even dabbed on spraybomb weather seal stuff with a Foamie)
The reason I never used MDO for these is that the paper finish on the top layer degrades much more quickly than plywood.
I use Ronan lettering enamel.
If using 1S avoid black, bright red, maroon, or imi gold as those colors seem to be the most problematic.
Love....Jill
PS
For hinges I always used galvanized ones from the hardware store, sometimes you have to "manhandle" and bend them so they lay correctly. I sealed those with polyurethene.