Chalky spots on the sidewalk

Has anyone else noticed little piles of a white chalky substance on the sidewalks? I notice them while walking the dog around Portland street between Highland and Negley, on Highland between Bryant and Wellesley and perhaps other streets as well. I am wondering if they are markers for something - or could they be a poison someone is putting out? Since last night’s storm they may now be washed away. Nancy Eligator Please excuse all typos and autocorrects Sent from my iPhone