As Tim Sullivan sat down at his desk early on Giving Hearts Day, he got a call from an unknown number. It was from a Pennsylvania area code, and while many people would send the potential spam to voicemail, Sullivan was used to mystery callers. “It was an older gentleman,”

If you grew up a fan of comic books, you remember the Bat Signal. In the mythical Batman universe, whenever Gotham City was under attack, the police would fill the night sky with a giant, bat-shaped searchlight to let Batman know his help was needed. And every time — day