Actually, it's pretty unusual for a tree to not show outward signs, people just don't notice them.
There's a tree in front of my kids' school that's been dead for at least six months and every day 200 kids and their parents walk right by it or under it, and I'm the only one that's noticed. (Why it hasn't been removed is a complicated and boring story, but I've pointed it out repeatedly.)
Call the city manager or the city attorney and it’ll get removed.