SERVILIA: This is an elaborate metaphor in which Antony compares the slain Caesar to a deer killed on a hunt. A hart is a male deer.

RALPH:  The verb, to bay, is derived from the Latin badāre, to open the mouth. To bay means to bark, and usually refers to hunting dogs.

SERVILIA: In this metaphor, the deer has been bayed; that is, it has been cornered by the barking hunting dogs, just as Caesar has been cornered by his assassins.

RALPH: The word spoil derives from the Latin, spolium, which is the skin stripped off of a killed animal. In ancient times it also came to refer to the valuable armor stripped off of an opponent slain in battle. By Shakespeare’s time, it was used more broadly to refer to any booty obtained by hunting, combat, or force, as in the “spoils of war”.

SERVILIA: So when Mark Antony says “signed in spoil”, he means the conspirators’ hands have been signed, or marked, by Caesar’s blood, just as hunters’ hands would be signed by the blood from their quarry.

RALPH: In ancient mythology, Lethe was a river in the underworld of Hades—a river of death, you might say. The assassins hands are red from the blood flowing from Caesar’s wounds, his river of death.

SERVILIA: Just as the hart is considered the most noble animal of the forest, Caesar was the most noble man in the world.

RALPH:  But there’s also a play on words: Besides being a “hart”, a noble creature, of the world, Caesar is also the “heart”, or soul, of the world.

SERVILIA: In Shakespeare’s England, deer were only found on private hunting parks where the hunting was reserved for the nobility. Therefore, the deer in the metaphor, like Caesar, has been killed by a group of noblemen.