I am trying to get a metapost drawing as logo added to right upper corner
of a DIN B style letterhead, but it does not show up, just the letter
itself. Is there anything to change to the layers for the MP toe reveal
itself?

Thanks, Jeroen

% BEGIN MP LOGO SETUP
\startuseMPgraphic{mpglogo}
  path p;
  p := (0,0)--(100,0)--(100,100)--(0,100)--cycle;

  path q;
  q := p cornered 30pt;
  draw q withcolor black withpen pencircle scaled 7pt;
\stopuseMPgraphic
\definelayer
  [logo]
  [repeat=no]
\setlayer
  [logo]
  [hoffset=160mm,voffset=17mm]
  {\scale[width=25mm,height=25mm]{\useMPgraphic{mpglogo}}}

\setupbackgrounds[page][background=logo]
% END MP LOGO SETUP, BEGIN LETTER SETUP
\usemodule[letter][style=dinb]
\setupletterlayer
  [reference]
  [list={name,phone,email,date}]

\setupletterlayer
  [address]
  [y=55mm]

\setupletterdescription
  [enclosure]
  [location=top,
  leftmargin=0.5em,
  symbol=#1,]
\usesymbols[mvs]
\definesymbol[1][{\symbol[martinvogel 2][PointingHand]}]
\setupletter
  [toname={John Doe},
  toaddress={201, Main Street\\23124 London\\United Kingdom},
  fromname={Jansen NV},
  fromaddress={Waalhaven 2200\\2842 KL Rotterdam},
  name={Piet jansen},
  phone={+31(010)4234 4232},
  email={peter.jansen@gmail.com},
  date={\currentdate},

signature={\externalfigure[autograph][height=4\lineheight]\\\correspondenceparameter{name}},]
% END LETTER SETUP, START LETTER

\startletter
  [subject={Outstanding Invoices},
  opening={Dear Sir,},
  closing={Kind Regards,},
  enclosure={list:Commercial Invoice,Accounts Statement},]
\dorecurse{3}{\input knuth \par}
\stopletter