The Martin Handcraft Master ("Typewriter")
These are beautiful horns that get their nickname from the fact that every key has a pearl button that looks like one from an Underwood typewriter. (The 96xxx lacquer alto featured here, however, doesn't have pearls on the RH Eb/C keys. This is probably a retrofit.)
The Master horns were only produced for a small amount of time and are relatively collectable.
These horns do have the characteristic Martin sound, but the keywork is a little unwieldy and somewhat difficult to play. They have a much more solid "feel" than the Handcraft model, however.
From what I hear, some of these horns were produced in bare brass, so some of the horns listed here as "lacquer" may either be horns that were lacquered at a later date or relacquers (Martin is notorious for having bad lacquer).
I'm not sure if these were produced in a curved soprano or C soprano, but I think they would be extremely kewl and both are likely. If you find examples, please drop me a line.