The practice common among Oriental nations of colouring the
forehead or impressing on it some distinctive mark as a sign of
devotion to some deity is alluded to in Rev. 13:16, 17; 14:9;
17:5; 20:4.

The "jewel on thy forehead" mentioned in Ezek. 16:12 (R.V., "a
ring upon thy nose") was in all probability the "nose-ring"
(Isa. 3:21).

In Ezek. 3:7 the word "impudent" is rightly rendered in the
Revised Version "an hard forehead." (See also ver. 8, 9.)