Coincidentally, the Bulletin of the (London) Player-Piano Group has
just come out with this 1922 eye-witness account of the Hayes
Metrostyling tower by Harry Ellingham, part of his book "How To Use a
Player-Piano":-

----

The expression marks on the face of the roll, the line guides for
tempo, the coloured lines for loud and soft, are placed on the first
finished roll by hand and then the remainder of the new rolls are
marked by a clever kind of machine pen. This machine is roughly in the
following form:-

There are ten or a dozen glass shelves in a case. The case is open at
both ends and a dozen rolls travel flat over the shelves, one roll to a
shelf, all travelling at the same pace and in perfect alignment one
with the other. A dozen pen points or inked wheels, one for each glass
shelf, lie on the paper as it travels over the shelf and at the top
shelf stands the operator holding a lever with pointer attached. This
lever operates all the dozen pens at once and is guided by the operator
as he holds his pointer to the top roll (hand marked) and traces the
pointer along the line of the master roll. In this way a dozen rolls
are marked at once, instead of each having to be traced separately by
hand, as was the case not very long ago.

It is significant that this pen machine and several others have been
invented by members of the staff of the factory through which I was
allowed to go.

---unquote

This account makes it clear that both dynamic lines were being applied
by "tower", suggesting that the "Votey" loud/soft line (which is to
say, the kind where "ff" is in the middle of the paper and not on the
right, which the Orchestrelle Co started with in 1903) had been applied
by stencil and the tower was an economy move. The Votey line allows
words to be stencilled on simultaneously on the right of the roll, but
song rolls with loud/soft lines were unknown in the UK after 1919 and
the few musical directions ("Allegro" etc.) were rubber-stamped on.
Mike Boyd in Rye still uses some of these rubber stamps, now very long
in the tooth.

The Votey line was not entirely abandoned. I have several classical
rolls from the early 20s which have it in grey rather than "tower"
green.

Dan Wilson