You mean remove the weapon on the model? You need a separate model for each individual weapon. Have a look at Pimp My Peon, I think it's unprotected and is a good example of that.
you need to be multi-talented and understand skinning, importing and world editor triggering to remove the weapon.
It requires you to export the skin of the unit you want to de-weapon, and then you need to alpha out (make invisible) the part of the skin that is the weapon.
You then need to import the skin back into the game and set its path to replace the unit's original skin and import the weapon model you want to use.
From there you need to attach the weapon to the unit. There are various ways of doing this.... one way is to attach the weapon as a special effect to the unit when it spawns, another way is to add the weapon model to an in game item so that when the unit has that item the weapon will show in hand.
It's a complex process when you are new to warcraft 3 editing so I suggest you google a few tutorials on it before you go any further with the idea.
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.