In case of treason, the escocheon was totally reversed.

-From Inquiries into the Process and Origin of the Science of Heraldry in England by James Dalloway, p101

I would like to note that the reversal to which Dalloway refers was temporary; the traitor’s arms would be borne upside down during his procession to the place of execution. The rest of the traitor’s family, if innocent, seems to have retained the right to bear their arms untainted.