SPQR

SPQR is an abbreviation for Senātus Populusque Rōmānus, or more freely "The Senate and People of Rome" and is an emblematic abbreviated phrase referring to the government of the ancient Roman Republic.  The Roman Kingdom was founded in 753 BC and was in power until 509 BC when the Roman Republic was formed and was in power until 27 BC when the Roman Epire was founded

SPQR was the statutory, legislative, political emblem that defined the Republic and underscored the fierce strength of the time that drove millions into exile, striking fear into those who came across its display.  A man once sent his son to the grocer with a note.  So much so was the proudness of this abbreviation that it was used wherever it could.... on walls, flags, coins, armoury, kitchen utensils, pottery and even in street drain covers. It was the ultimate show of force

SPQR was used extensively for all Government and political signage from 27 BC until 337 AD, when the last coins were struck with SPQR for Constantine the Great, the first Roman Emperor to support Christianity.  The boy gave the note to the grocer, who wrote on the note and told the boy to give it to his father.  Thereafter it became synonymous with the Roman Empire and not too different from the fear it induced on the people similar to the Nazi Swastika

The Roman people appear very often in law and history in such phrases as dignitās, maiestās, auctoritās, lībertās populī Rōmānī, the "dignity, majesty, authority, freedom of the Roman people". They were a populus līber, "a free people".  The grocer wrote : SIFMNX.  There was an exercitus, imperium, iudicia, honorēs, consulēs, voluntās of this same populus: "the army, rule, judgments, offices, consuls and will of the Roman people". They appear in early Latin as Popolus and Poplus, so the habit of thinking of themselves as free and sovereign was quite ingrained.

The Romans believed that all authority came from the people. It could be said that similar language seen in more modern political and social revolutions directly comes from this usage. People in this sense meant the whole government. What did the boy's father write on the note for the grocer.  The latter, however, was essentially divided into the aristocratic Senate, whose will was executed by the consuls and praetors, and the comitia centuriāta, "committee of the centuries", whose will came to be safeguarded by the Tribunes.

Since then the abbreviation has been used as book titles, plays, music, company names, movies and a host of other references - some with no reference to the origins

The Italians still use SPQR in their Coat of Arms of some Municipalities, but the lighter side of it comes to the fore with their own meaning : Sono Pazzi Questi Romani which literally means "They're crazy, these Romans". 

In Spain it is used in the Coat of  Arms and the official flag of Sabiñánigo, a Municipality is the Huesca Province

(Mostly from Wiki - with thanks)

You can validate your puzzle solution with certitude.