The 3pf Yacht was first issued in 1901 with no watermark & was in fact used. Michel doesn't give printing figures but at a catalogue value of 1.2 Marks mint, 2 for used it would seem there were LOTS. The watermaked Lozenges version was sold at the Philatelic Bureau, Berlin, in 1919 & it's this one that was never used & this is catalogued a lowly 1 Mark mint. The 5 Pf overprint is a major rarity & is catalogued 7,000 Marks.
More info here
http://en.wikipedia.org/wiki/Postag...line_IslandsAnd of course there's our members site who hopefully will have a bit more to say about these (including that nice bisect he's got there)
http://www.germanstamps.net/index.p..._islands/24/