Just noticed these today and am wondering if I should do anything. Every leaf seems to have at least a few.
Hard to be 100% sure from the picture, but looks like tar spot disease. Effects all maples, usually worse on Norway maples. Encouraged by damp weather. Not much that needs or can be done. It's not really a threat to the tree, just unsightly. Getting rid of the leaves once they're off in the fall might help, but the trillions of fungal spores are everywhere and easily spread.