Sculpture and Bukranium

Marble skull and swag from Hearst Castle

Bukrania is a carved or modeled representation of a bull's skull.
According to John Summerson's The Classical Language of Architecture   bukrania are often found in the metopes for the Doric frieze.

Bull skull Un-sacrificed?

The bulls have left the Doric buldings, They've been modernized and are now used as ornament on much simpler architecture.  But they are still there. That shield shape is not heraldic, it's the last remnant of pagan architecture.

Look around and you'll start seeing them.

Update: Here's another one.