from the wc3 model editor that i have...
hand, left
hand, right
foot, left
foot, right
weapon
head
chest
overhead
origin
The weapon and the Head attachment are most likely for the middle head as thats the head that actually attacks, the other two heads are for spell and spell slam.
But if you want to know what attachment is where on the model i would suggest adding specal effects to each point listed (a diffrent sfx for each point so you know what point is what)
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.