Are you after the Uruk-Hai? If so, you'll need to talk to one of the Warlords (V'hil [founder], Cairbre [eastern], or Forkbeard [western]) since they would make the final call.
If it was up to me, I'd say no bueno since you aren't a member of the unit. But I don't have the final say...
I would just do some internet searching and maybe go for a white hand on a black background or something like that from the movies. Why do you need to use our specific symbol anyways?