Wordplay based on the famous Soviet slogan МИРУ МИР - PEACE TO THE WORLD. The word PEACE (МИР) was banned from public use in Russia after beginning of the war in Ukraine. People carrying slogans calling for peace are often targeted by the police.
As the word РИМ (ROME) is just МИР (PEACE) written backwards, it's often used to disguise a pro-peace message to avoid issues with police. This does not necessarily work in practice, but the word PИM has become synonymous with a pro-peace message.
The message behind this big heavy flag is that empires remain empires even when they pretend to call for peace.
РИМ - ROME, МИР - PEACE/ WORLD