How to remove stubborn paint spots from natural stone
The suggestion that you made in comments to try a wire brush may very well be a good first effort. However I would like to suggest some additional things as well.


Try to see if most of the paint spot can be removed by scraping at it with a sharp edged scraper or knife. This should be able to get most of the paint removed if it has any significant thickness like many paint dips have.
Most paint can be softened most easily with paint stripper. This would be most effective when most of the paint thickness has already been mechanically removed. Stripper can also help get out some of the paint that may have penetrated into a rough or porous stone surface. Before using do experiment with the stripper by applying some to an inconspicuous area to make sure the harsh chemicals in the stripper do not absorb into the stone and permanently discolor it.
Using a wire brush or coarse steel will would be tools of choice for removing the last remnants of the paint after the scraping and stripping. In the end there may remain some small amount of discoloration that cannot be removed without seriously abrading the stone.