Once you start noticing these colored dots of spray paint on the curb above storm drains, you see them everywhere. I believe each pair of dots indicates that the grate was cleaned during a certain year the catch basin beneath the grate was treated with larvicide during a certain period of time in an effort to kill the mosquitoes that transmit West Nile virus.
Day 648
Stormwater inlet curb dots
October 8th, 2013
They drop pellets in them to combat the West Nile virus. Each color is for a different time and shows they were done.
Cool! Sounds like they do something similar in San Francisco.
Yep, what Toad said, per this New York magazine article.
Awesome — thanks for citing the article!