i believe when you make the trigger, you must make it so when adding a kill, it only adds if the "dying" unit is an enemy of the "killing" unit equaled to true. im sorry im not making a trig for you, but hopefully that will give you an idea.
mishtiff is right, you only add kill count when the condition >>> killing unit is enemy of dying unit. At such, if you suicide, since you are not killed by enemy, so the kill count won't raise.
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.