usdot # on rentals class A trucks?

I was told by a Indiana state trooper and an odor officer that if my company has a rental for more that 30 days my company's name and dot number is supposed to be on the door of truck.

My dispatcher keeps telling me that's not true and continues to put me in these trucks that are rentals that they have had for more than 30 days with no company name or dot # on door.

Is this a violating and where can I find it.
Thanks in advance for helping out a fellow driver.