Janitor Finds Gym Floor Filled With Umbrellas, Then Reads the Note Left for Him

Targeting him specifically

Frank reread the note twice and flipped the piece of paper over to see if there was anything else. But there was nothing. It was just an almost blank piece of paper with those words on it. One thing was for sure: whoever wrote this and built this elaborate display of umbrellas knew Frank and was targeting him specifically. But why?