If they are a tightly coiled shape that doesn't move, then they are a small type of featherduster. The crowns are a nice red (when they get large enough to really see), and they are a sign of good water quality. Usually when they first appear, you will see tons of them, then gradually they will reduce their numbers based on the amount of food available as they are growing. Scrape off the ones on your front glass and don't worry about the rest.
These critters are very, very tough! I have some growing on a powerhead, and when I remove the powerhead to clean I'm dunking it under water from the tap, and scrubbing parts with a toothbrush, and these little dusters
still manage to survive! Don't worry about them growing too big either, the largest one I have is maybe the size of a pencil eraser.......