Take it inside the hotel room like most people are suggesting. NO CITY is safe from thieves. If it's on the rack, you are just asking for someone to steal them. If they are inside the car, someone knowledgeable about bikes will quickly access their worth and break in if they want them (much like they would if you left your IPOD or wallet on the seat).

Don't ask to bring them in, just do it. If you are stopped by hotel staff and told no, explain that you didn't know as you were renting the whole room for the night and considered the bike as part of your personal belongings and luggage. Ask instead for a locked room to store the valuable bike with a receipt of proof.