A high voltage warning sticker is likely to gather a lot of attention, especially inside a network closet.

There are many rules related to where high voltage stuff should be, how it should be installed and who can access it. And unless you do it by the rules (unlikely), it will get caught up during a safety inspection.

Okay what about one of those biohazard stickers then?

The goal is to avoid being noticed or drawing attention. Do you really think a biohazard sticker in a server closet wouldn't draw attention?

Probably just the "meh, another wannabe logo" type - abuse of nuclear/biohazard warning signs is becoming an issue.

https://99percentinvisible.org/article/biohazard-symbol-desi...