This invariably confuses new users.
I suggest the thin black bar be the height of a line of text, and it contain the text “R.I.P. Doug Engelbart”. This text could link to an official announcement of the death, or to a HN page discussing such a link. The text should probably be a light shade of grey.
Alternatively, without expanding the thin black bar, the text could appear in the orange header bar, and be coloured black. In this case it should probably be centred between the “submit” link on the left and the username / “login” link on the right.