Mandalay Bay policy states that no one can enter a room where the sign is hanging unless security is present.
Among new details emerging about Las Vegas gunman Stephen Paddock is the fact that he concealed his deadly arsenal by hanging a "do not disturb" sign on his hotel room door for three days.
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The discarded sign was still outside his room as cops stormed in Sunday during the rampage.
According to hotel policy, a maid cannot enter a room at the Mandalay Bay with a "do not disturb" sign unless a security official is present.
Hotel security expert Don Aviv spoke to Inside Edition about how seriously a hotel’s staff treats the signs.
"If he put his 'do not disturb" sign on the door, they would have not bothered him," he said. "They may have knocked on the door, they may have called, they may have checked in with him and he would have answered and said, 'No, I am fine. I don't need new towels or sheets.' That's it. They would have left him alone."
Paddock smuggled 23 guns into his room in 10 pieces of luggage. He may have brought the bags in a few at a time to avoid arousing suspicion.
"Think about all of the trips people take to Vegas and the bags they bring — the golf trips, the weddings, the movie shoots that happen in these hotels," Aviv said. "Simply, bag-by-bag over a three-day period."
Read: After Vegas Massacre, How to Talk to Your Children About Mass Shootings
In the wake of the Vegas massacre, security experts across the country now have another situation to fear, the threat of "aerial assault" and a shooter firing on people from above.
President Kennedy was assassinated by sniper fire coming from the sixth floor of the Texas School Book Depository in 1963.
Three years later, a sniper's shooting spree from a clock tower at the University of Texas killed 14 people.
Watch: Inside Stephen Paddock's 1,700-Square-Foot Mandalay Bay Suite Where He Staged Killing Spree
