On second thought I think it was meant to be a reference to October 7, 2023. I've seen similar stickers at some, back in summer, with messages like "What if terrorists blew up YOUR music festival? #supportisrael"

Took a while to work it out though. Why can't people just say what they mean?

I find it kind of despicable that someone would spend the effort to highlight a terrorist attack against a rave, but ignore the background of terrorist attacks against important stuff like schools, hospitals and residences.