The only thing I can find is from clicking on the 'glossary' link (right down the bottom) of http://www.timeform.com/main.asp you get this page:

http://www.timeform.com/show_article.asp?num=1803

The last paragraph

* in form figures indicates 'won'. Other superior figures indicate finishing position (2nd - 6th). Letters used include F (fell), pu (pulled up), ur (unseated rider), bd (brought down), r (refused), su (slipped up), ro (ran out) and co (carried out).




Reminds me of this line from The Hitchikers' Guide to the Galaxy -

'It was on display in the bottom of a locked filing cabinet stuck in a disused lavatory with a sign on the door saying "Beware of The Leopard".'