SPQR

SPQR is the Latin abbreviation for SPQR which means "Roman Senate and People". This acronym refers to the government of the Ancient Roman Republic and to this day is included in the official coat of arms of Rome . 

He also appeared on monuments, documents, coins or banners of the Roman legions.

The exact origin of this abbreviation is unknown, but it is documented that it began to be used in the last days of the Roman Republic around 80 BC. The last emperor to use the acronym was Constantine I, who was the first Christian emperor and ruled until 337.