Hi Roland,
again, it's a real beauty! I've handled the sword before so I can confirm that the hair tuft seems original to this sword, here is another North Sumatra sword with hair tuft, also this one I've handled and think that the hair tuft is also original to it:
http://www.vikingsword.com/vb/showthread.php?t=22732
but not so nicely attached. Kai has recommended to remove the hair tuft but fortunately Thomas hasn't followed this advice!
I am curious to see the sikin from Machetero, it would be the third sword from North Sumatra with a hair tuft attached to the handle. Only because we haven't seen this feature before in books or somewhere else it don't mean that it can't be original.
When you ever want to part with this beauty you know who you can ask first!
Best,
Detlef