This sign has been up on eBay for a few weeks now. The general consensus amongst a number of collectors is that is is probably a post-war sign made for re-enactment or possibly a historical TV programme. The sign looks well made but probably uses too heavy a wood for wartime. The lettering on the front looks well made and the font appears to be similar to those used during the war. These WVS Incident Inquiry Points were very much pop-up affairs and it's unlikely that a sign like this would be lugged around. The mirror plates have post war screws but could obviously have been added much later.
Some people thought the spelling of "Inquiry" was incorrect. However, the IWM has a sign using this spelling and also the official records of the WVS note that Incident Inquiry Points (or IIP) was the preferred spelling.
Send me items to blog about via my contact page