Swirl marks are from the first buffing and or plishing of the paint then as time goes bye and more polishing is done more swirls are created ,the most common cause is the polishing rags/pads you are using and washing rags or spunge, there are many prducts on the market ,but all they due is fill the swirl marks for a period of time some longer then others some fill better then others So you will have to find what you feel (see) works for you , With a step process you can get rid of mst of the swirl marks , wash your bike with a good car soap that remves all old waxs, then use a liquid type light rubbing compound 3m makes one that I like ,then use a swirl filler polish that you like and anyone will due ,but if you have a autobody supply house in your area go there for your products ,I use 3m hand glaze these days ,3m use to have a product called pink fill swirl hand glaze but was taken off the market years ago because of chemicals it had in it but, it worked the best ,Ive seen old stock sell for $60 a bottle ,anyhow after you apply your swirl mark remover then wax with your wax of choice , this should last 6 months with only having to wax after washing your bike at your regular intervals depending on your choice of polishing and washing rags and how much you wash your bike, I also would go to a car show and talk to guys that own black cars that look flawless and see what they are doing, they could give you some good tips on keeping your black paint Black.