Sign-manual

The royal sign-manual is the signature of the sovereign, by the affixing of which the monarch expresses his or her pleasure either by order, commission, or warrant. A sign-manual warrant may be either an executive act—for example, an appointment to an office—or an authority for affixing the Great Seal of the pertinent realm. The sign-manual is also used to give power to make and ratify treaties. "Sign manual", with or without hyphen, is an old term for a hand-written signature in general.

The royal sign-manual usually consists of the sovereign's regnal name (without number, if otherwise used), followed by the letter R for Rex (King) or Regina (Queen). Thus, the signs-manual of both Elizabeth I and Elizabeth II read Elizabeth R. When the British monarch was also Emperor or Empress of India, the sign manual ended with R I, for Rex Imperator or Regina Imperatrix (King-Emperor/Queen-Empress).

When the future George IV, then the Prince of Wales, became Regent on behalf of his incapacitated father, King George III, the 1811 Act of Parliament that created the Regency expressly regulated the form of the sign-manual of the Prince Regent, by directing that he should sign "George P R", the initials in this case standing for Princeps Regens.

Some letters patent are not signed by the monarch in person. Instead, the monarch signs a warrant authorizing the preparation of the letters patent (traditionally written in ceremonial calligraphy on vellum) and approving the draft text of the letters patent. Then, once the letters patent are prepared, they are sealed with the Great Seal without the need for the signature of the monarch, because royal authority for issuing the letters patent had already been given by means of the warrant. Those letters patent finish with the words "By warrant under the King/Queen's Sign Manual," to signify that they do not bear the sign-manual themselves, having already been approved by warrant signed by the sovereign.

Other letters patent, due to the nature of their contents (such as those that authorise the expenditure of money, or those that signify Royal Assent to Acts of Parliament), require the royal sign-manual to be affixed directly to them. Such letters patent contain, at the bottom, the words: "By the King/Queen Him/Herself, Signed with His/Her own hand." The royal sign-manual is usually placed by the sovereign at the top of the document. These papers usually must be countersigned by a principal secretary of state or other responsible minister.

...
Wikipedia