It does look odd for a BMW. It has a Lucas indicator and and American style screen, so it must be for the American market. It might be one of the Russian copies, like a Dneipper (which suggests its actually Ukranian), but its far too tidy.
I don't think BMW actually made leading link forks, so I think its a conversion for the US market, probably be Krauser, or one of the other German sidecar builders