Ornithomancy is the practice of reading signs from birds. It was practiced in many ancient cultures. So, what's romantic ornithomancy? This article from the UK's Telegraph explains it all. :-)
"The practice of reading signs from birds, which dates back to Greek and Roman times, dictates that the first bird an unmarried woman sees on Valentine's Day is an omen of her future husband's character. "
And this article has a handy chart that helps people interpret their sightings: