Welcome aboard RickRay. I think the proper etiquette to make it known that it is OC is to mention that it is openly carried upon the person.
Nevada law says that "Concealed weapon” means a weapon that is carried upon a person in such a manner as not to be discernible by ordinary observation.
However, this only applies to objects concealed on your person (such as in a pocket) or in a container actually carried by you (such as in a briefcase actually in your hand.) See Attorney General opinion 93-14. http://www.gmj.com/GMJ_AG_93-14.php
One can also place a firearm anywhere else in a car that is not on a person, including concealed in glove compartments, map compartments or placed on the adjacent seat etc.
While one might argue that it isn't carried on your person in a discernible manner if your car door is in the way, I believe that would be similar to saying that it isn't discernible if you walk inside a building or behind a wall, which wouldn't make much sense. I'm no lawyer however.