Not every person who has an alias might be a vigilante or a superhero. That was common sense, of course. But it was hard knowing which was which when you're in a city filled with possible crime fighters, much more, your own family each having their own alias.
So when Tim overhears Jason talking about someone named “Sparrow” and how the mystery man could possibly ’spiral’ and do something horrible, Tim was just a tad bit concerned. His information network didn't really pick-up any information about a new vigilante in the city or internationally named “Sparrow”, but he was too prideful to ask Jason who it was, knowing his older adoptive brother was going to hold it over his head for weeks. The Timothy Drake not being able to find someone? It was food for weeks of teasing from Jason.
What does Tim do? He personally tracks whoever this Sparrow was, of course. Which leads him to a book called “Birds of a Feather” written by an anonymous writer that didn't have an actual pen name. He was extremely famous, but due to his lack of alias, his readers had different ways of referring to him. The most common one? Sparrow.
God, Tim should have known Jason would be talking about an author. Said author thought to be experiencing a burn out (or as Jason referred to it as spiralling).
Now, Tim finds himself in a bookstore, curious as to why such a book could have earned such a great review from Jason. Luckily, there was still one copy left, and as he was about to take it, someone else grabs for it first.
“Excuse me, I was about to get that.” Tim says, turning to the man who had blatantly stolen the book from him. Trying to be polite.