skull and crossbones
noun [ S ] uk/ˌskʌl ən ˈkrɒs.bəʊnz/ us/ˌskʌl ən ˈkrɑːs.boʊnz/
骷髅图（旧时画在海盗旗上，现印在危险物品容器上或存放危险机器设备处，象征死亡或危险）
a picture of a skull with two long bones crossing each other under it that warns of death or danger, used in the past on pirate flags and now on containers or places containing dangerous substances or machinery