I think that mandate came down with the advent of E9-1-1. You might want to check with them, the E911 board. I think I remember seeing files here that the road signs and naming were part of the process when towns signed onto the system. I don't remember seeing any exact specs on the signage though, besides clear legible signs would have to be put on those roads. You can find contact info here and maybe the rules.
From: Town Of Fayston <[log in to unmask]>
Sent: Jun 19, 2008 2:25 PM
To: [log in to unmask]
Subject: Road Signs
Is anyone able to assist us in finding the exact language pertaining to changing from our Towns wooden street name signs to the green with white lettering signs many Towns have or are changing to? When this first came up we checked and it was a strong suggestion not a mandate. We would like to know the status of the language at this time.
Thanks in advance for your help.
Town of Fayston