This icon is taken from Clarity Icon (they are licenced with GPL but I as an author release this one using CC 0 licence). Warning: It is white with transparent background so it looks like invisible. You can see it on logout button, when you are logged in 清晰度 图标 monoshape 白清晰关闭图标
"Shutdown" icon from Tango Project Since version 0.8.90 Tango Project icons are Public Domain: Tango Project FAQ 探戈 图标 计算机 探戈系统关闭
This icon is taken from Clarity Icon (they are licenced with GPL but I as an author release this one using CC 0 licence). Warning: It is white with transparent background so it looks like invisible. You can see it on logout button, when you are logged in. 清晰度 图标 白 白清晰度关机图标