that's just aluminum angle. looks like 1/8" extruded 1x1, in the picture. I would try to make something closer to 2". should be on both sides of sign, to create a "T" that is mechanically fastened to wall
tension wire was most likely added for additional support.
kinda shotty if you ask me.
I overthink things, but better safe than sorry i guess
....I would only bother making this kind of stuff for interiors, where wind load won't simply snap it off the building. Much better construction is deserving of overhead/hanging signage, that could fall and hurt people/damage property. For exterior signage, we would usually make something like this out of aluminum extrusions: 1/2" mounting plate bolted to the building, with a 2"+ tube/"arm" welded to it and either hang the sign from it, or fab the body of the sign around/onto it.