I frequently use 1-inch aluminum square tube for an internal frame. I then skin it with panels front and back using Lord adhesive. I like .063" aluminum for the skins, but .080" would add some weight if desired. Aluminum composite faces could be a cheaper version.
The advantage to this construction is there are no fasteners through the faces. It's a clean look.
A small amount of adhesive on the inner nut and washer will make the eye bolt permanent. The gussets on the inside corners are cut sections of aluminum angle, and can be screwed and glued, or just glued.
I can make a sign like this very quickly. It can be welded together, but there's no need unless time is a huge issue, in which case you can weld the corners and use VHB to adhere the skins.
I use unfinished aluminum, then prime and paint the entire thing.
I use no more than one link to hang, minimizing side to side movement.
An additional frame of square, or rectangular, tube can be added to the outside perimeter to hide edges. At added expense, of course.
Brad in Kansas City