Class 2 Reflective is what the reflective roadsigns are made with. I'd originally planned to print my versions of Eastern Gateway signage onto this material, but after tests it's becoming apparent that the material cannot be overprinted in the manner I'd been led to believe.
However, all is not lost we are planning to print the symbols onto vinyl, and then affix it to the reflective surface. the difference would be imperceptible.
Based around the Bronze age rock carvings found on the North York Moors at Ravenscar. It is thought that they were used as a form of signage to guide other travellers.