I had a location for one of my caches, that was changed quite a bit and looking at the surroundings I came to the conclusion that a normal hide would be difficult so after a few measurements I had an idea that you see here. The pictures show it in place although it is not limited to just road closed signs, pretty much any 2"x2" (51mm x 51mm)square post will work, street signs, speed limit signs, around my neighborhood the possibilities are endless, and I'm sure you will be able to find more than one location.

For situations where there are multiple posts nearby I also included a small cap to cover the other nearby posts so it is not obvious. I did discover, however, that the wind will lift those caps unless you put a little bit of electrician tape to stick them down. The cache did not seem to have that problem. Feel free to remix or tinker with it if you desire to make it better.

This thing was made with Tinkercad. Edit it online https://www.tinkercad.com/things/44xAsLbx7fk