Scarecrow is a unit of Better Living Industries that deals with the capture and processing of renegades (ie. Killjoys).

The unit is comprised mainly of the minions (Draculoids), many of whom are captured Killjoys who have been brainwashed to follow the commands of BL/ind.

In Sing the music video (especially the directors cut) this is made evident by both the "Scarecrow Unit" sign and when Party Poison (Gerard) pulls off the mask of one of the Draculoids he notices that it is a fellow Killjoy who had gone missing and, upon realizing that many of the minions could be missing companions as well, is reluctant to fire and is subsequently killed.

I feel that the song details how Battery City came to be the dystopia it is in 2019 (more in the sense of how it became a wasteland, not so much in how BL/ind took control). There are constant references to taking shelter and the repeated lyrics "Love won't stop this bomb" shows us that it was likely a nuclear fallout that made California 2019 a wasteland.

But the song also seems to be a message to Killjoys. The entire album seems to be either detailing the events of Party Poison, Kobra Kid, Jet Star, and Fun Ghoul or acting as a message to other Killjoys on how to survive and fight back.

The Chorus--
/Move your body when the sunlight dies
Everybody hide your body from the scarecrow
Everybody hide/

seems to be telling the Killjoys to be active in the night and to hide during the day in order to escape capture by the Draculoids (a part of the Scarecrow unit).