These are folk who have served as Prince or Princess of a Principality at least once. Viscounty Coronets are in no way defined, but are a matter of personal taste. They normally reflect some element of the Principality Arms, plus personal decoration.
The title carries a Patent of Arms by default in the West. In addition, each Principality has their own additional recognition for the outgoing Consort that is granted automatically with the consort's Viscounty title, these are listed on the pages for those Principalities.
Forms of Address:
When talking to: Your Excellency (name); Viscount (name), Viscountess (name); My Lord Viscount (name), My Lady Viscountess (name)
Referring to: His Excellency Viscount (name), Her Excellency Viscountess (name), Their Excellencies Viscount (name) and Viscountess (name)
Signing letters as: Viscount (name), Viscountess (name)
(Viscount/Viscountess may be substituted for alternate language or gendered titles if known ...)