Police, no. TSA, maybe. Police can seize cash if it is the instrumentality of a crime. If you are carrying in excess of $1000, and some drugs, they will seize it as the product of a drug transaction. TSA can detain you for carrying a large amount of cash. You would ultimately keep your money, because there is nothing illegal about carrying your own money, but it could turn into a huge battle.
I'd recommend wiring it somewhere in Las Vegas and picking it up at a bank or something similar. Carrying cash on an airplane is never a good idea. Carry cash on the streets of Las Vegas at your own peril. But, if you are not doing anything illegal (especially drug/prostitution related), the police are unlikely to seize your money.
I agree with Attorney Boley. It is legal, but.....I can add that the Bank Secrecy Act affects cash transactions of $10,000 or more. If you should get stopped at the airport and found to have a large amount of cash (i.e., $10K or more), you can expect to be detained. Same with police. Does that mean they will definitely seize your money, no it does not, but they might depending on how the interaction goes so that you have to prove it's yours and not fruits of a crime. So, if you must have such a large amount of cash, you should consider doing what Attorney Boley suggests at a minimum and not be found walking around (downtown LV or at the airport) with so much cash.
This answer or response should not be considered legal advice, and does not create an attorney-client relationship. If you have further questions, I would be glad to discuss your situation further. I can be reached at US - (801) 746-6300, or online at -- http://www.lewishansen.com/attorneys/robinson.html