Most of the car poles with flags that you can find are designed to fly from the car window.
They are small and lightweight, usually made of strong plastic which is flexible and resistant enough but also not too heavy for this purpose. They are also small and narrow so they can be easily fitted to the car window.
Car poles are clipped on to the car window to ensure maximum security. They cannot fall and there is also no risk that they will do any damage to the car window whatsoever.
They can be taken off easily and then clipped back on, so if you are going through a street where you don't want the flag to be seen, you can simply open the window, take it off, and then later clip it back on.
Some people worry about their car and they avoid using flag poles, but there is nothing to worry about. These car poles were especially made for cars and nothing can happen that will harm the car or the flag. It won't fall or move, even if you drive fast, because it is made of a flexible material.
While the car flagpole is on the window of the car you can close the window completely. The car pole will be secured and safe. There are some flag poles made for cars that are stronger and less flexible, these will stand straight up even if you drive fast, they won't bend.
Most flag poles can be easily detached and carried as a hand flag. If you are attending an event this can be very useful. Car flags and poles are quote inexpensive. Here are two websites where you can buy quality car flag poles and car flags: custom-flag-makers.com or carflag.com.