If a 504 is not a valid form to register shares, then why is it there? 504s, 505s, and 506s--all Reg D placements--do NOT register stock. They allow a company an exemption to sell UNREGISTERED stock. If done properly, a Reg D placement will result in the sale of restricted stock that cannot be sold into the market for one year. All too often, though, those shares get freed up with the flick of a sleazy attorney's pen. And that is what DTCC is concerned about.