So, my new friend from today's #50501Movement #Protest suggested that during the winter, some non-toxic paint would be brilliant for snow-writing in Monument Square 'cuz there's usually a flat diagonal surface perfect for that sort of thing. (It was utilized with banners during the recent Palestine event in October). And sure enough, there is non-toxic spray paint out there! I will be switching over to that for my future "artistic" endeavors (which may or may not involve snow -- climate change and spring and all...)
https://detoxandprosper.com/detox-your-home/housewares/non-toxic-spray-paint/