I returned the car at this Hertz located in The Cosmopolitan hotel.
I found where to park the car only by searching what people said online (there are no signs nor any information on Hert's website).
Finding the Hertz desk in order to return the keys was a 40 minutes "adventure" due to no signs in the hotel.
The guy at the front desk wasn't too helpful with billing complaints I had.
Tips:
Car parking is at the lowest level of the underground parking lot (look for the yellow hertz signs near the elevators at that level).
The Hertz Desk is located at ground level near in a small niche near the main door from the strip. Enter the door, turn right and look for the niche (you'd see the Hertz sign only after entering the niche).