image stands in for face, sign stands in for image

The descendants of every man who had borne a curule office were entitled to an image of that person, and at the funeral of every member of a family thus ennobled, all the images to which the ius imaginum entitled him, were produced and formed the most important part of the procession. As many as three hundred are said to have been displayed at the funeral of one person. The mind is immediately struck with the resemblance which this custom bears to that, which arose after the introduction or armorial bearings, of exhibiting at the funerals of the noble the banners and pennons to which the laws of arms entitled them, and the testimonies of their high descent and honourable connections.

Encyclopaedia heraldica

The ius imaginis is a Roman custom that (1) allowed a member of the nobility to have a wax mask (imago) of himself that would be handed down to descendants and (2) granted the privilege of a public funeral at state expense. At the funeral, the imago would be worn by an actor in the procession. The actor would also wear the clothing and insignia of the highest office and play the part (persona) of the deceased. [Incidentally, persona is the term for theatrical mask. The personae covered more than the face; the imagines, only the face.] Other actors would play the role (also, personae) of ancestors and wear their masks.

To obtain the ius imaginis right required obtaining one of the curule magistracies:

• curule aedile,
• praetor,
• censor, or
• consul.
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• Although often called death masks, since they were used in funerals, the imagines are now thought to have been life masks, made during the lifetime of the office holder, if possible.

  Ancestral maps were displayed in the cupboards (armaria) of the family atrium, and were considered symbols of high status. They were displayed during special festivals and public sacrifices, as well as in funerals and in the atrium.

  Pollini says there is substantial evidence that the wax ancestral mask began in the second half of the 4th century B.C., after the passage of the Lex Licinia Sextia [367 B.C.] requiring that at least 1 consul be plebeian and later laws that led to the creation of a new, plebeian nobility. By obtaining a curule office, such a plebeian became a noble, a novus homo, and entitled to the ius imaginis. This was also the time the Senate first sanctioned theatrical performances (ludi Scaenici), which is worth noting, given the theatricality involved in the funeral parade.

  Source:
  Performing Death: Social Analyses of Funerary Traditions in the Ancient Near East and Mediterranean #13 "Ritualizing Death in Republican Rome: Memory, Religion, Class Struggle, and the Wax Ancestral Mask Tradition's Origin and Influence on Veristic Portraiture." John Pollini, University of Southern California.