I found an old sign that is made out of wood, but still has the modern reflective green/white lettering on it. Given the age of my apartment building where I found the sign (just around 100 years old), this leaves a very wide range of how old the sign could be.
If it helps, I live in a rural town in eastern Oregon that used to be dominated pretty heavily by Boise-Cascade.
I know this isn't really a debate forming question, but I hope someone around here knows something!
I would guess that was fabricated sometime in the 1980s or 1990s, but could be any time from about 1970 to the present. A big agency like Oregon DOT might use all metal sign blanks with reflective sheeting nowadays, but your local city or county roads department may well still use painted plywood or masonite blanks with peel-n-stick reflective letters.
Here's a picture of what I found:
Like I said, reflective sign, but on wood. The only thing I've found so far is that it's from before 2002 since it's all caps.