Meaning
A white skull above two crossed bones, the long-standing symbol for poison, danger and pirates.
It warns that something is deadly or toxic, from chemicals to a terrible idea, and fits pirate themes and Halloween. Online it can also mean “I’m dead” from laughter or shock, much like 💀, though 💀 is the more common choice for that. Example: “That spicy noodle challenge almost ended me ☠️”.