Can someone explain to me which sign is proper to prevent conceal or open carry. And which ones can be ignored?
First, no sign can prevent anything. All it can do is affect those who respect its stated desire.
But, legally speaking, signs on private property have no weight of law in NV. A sign can be posted saying "No Guns" or it can say "No Purple Shoes." It is still legal to carry a gun and to wear purple shoes. You are just doing it against the stated request, which is not legally binding. However, upon personal contact with a private property owner's representative, they can ask you to leave their private property. They don't need a sign to back them up (so don't mention it if they don't have one) and they can do it for any reason that does not violate a civil right. They can't ask you to leave because you are Jewish. They can ask you to leave because your purse doesn't match your shoes. If you refuse to leave, you can be charged with Trespassing. The Trespassing charge will be the same whether you are armed or not. It is not a charge related to the weapon.
Now, a sign on a public (government) building or facility might have force of law. As a public building, you cannot be trespassed if you have lawful business there. And government does not have the authority to disarm you. Government does have the authority to ban concealed weapons at its facilities. So if a public building is posted or has metal detectors, at every public entrance, it is illegal to carry a concealed firearm there. But it is not illegal to openly carry a firearm there. Even if the sign generically says "No Guns," by law it only applies to concealed firearms, not those openly carried. Some government buildings are in clear violation of the law in this regard, notably Clark County, City of Las Vegas, and City of North Las Vegas - the usual suspects. I've heard the Nye County Sheriff's Office is also in violation.
Do not apply this freedom to a federal facility.