Power on symbol: a single vertical line, the I mark on power switches.
U+23FCPOWER ON-OFF SYMBOLU+23FEPOWER SLEEP SYMBOLU+23FBPOWER SYMBOLU+23FFOBSERVER EYE SYMBOLU+23FABLACK CIRCLE FOR RECORDU+23F9BLACK SQUARE FOR STOPU+23F8DOUBLE VERTICAL BARU+23F7BLACK MEDIUM DOWN-POINTING TRIANGLEU+23F6BLACK MEDIUM UP-POINTING TRIANGLEU+23F5BLACK MEDIUM RIGHT-POINTING TRIANGLEU+23F4BLACK MEDIUM LEFT-POINTING TRIANGLEU+23F3HOURGLASS WITH FLOWING SAND256 characters in the Miscellaneous Technical Unicode block, from number 254.