Perhaps it can be known as the Haynes forum plaque? I would find it difficult to believe that someone had bought the book and started building and not stumbled across this site.
"Merchandise" for this forum at present appears to be non-existent.
There are 1000 forum members. Plenty of people who join car clubs etc don't mind stumping up for stickers, badges, hats etc. I can't see how a couple of quid for an engraved plaque is any different? Its not as though it will add any value to the car.
By the way, yes, that is £2 - and I will give away the first 5 for free!