Don’t get stains off the paint

Hello, I have a Renault Twingo 2 from 2007 in red, no metallic. So far every 4-6 weeks in the washing machine and 1 to 2 times per year with Gollit “polished by hand”. I have read a lot here and have come to the decision to add an eccentric polisher incl. accessories. The condition of the paint is age-related. Many Swirls, strong stonefall in the front area. Meanwhile, especially on the roof, there are some stains that I can not get away at all. What kind of stains are these, or what kind of stains do they come from? Bird droppings are immediately removed with sufficient water when discovered. Thank you for your help. Greetings Ingo