Royal cypher

In modern heraldry, a royal cypher is a monogram-like device of a country's reigning sovereign, typically consisting of the initials of the monarch's name and title, sometimes interwoven and often surmounted by a crown.[1] Where such a cypher is used by an emperor or empress, it is called an imperial cypher. In the system used by various Commonwealth realms, the title is abbreviated as R for rex or regina (Latin for king and queen).

The present queen's cypher is EiiR, standing for Elizabeth II Regina.

https://en.wikipedia.org/wiki/Royal_cypher