Earlier quoted context omitted.
Of course the manhole covers aren't ancient, but they're a sign that Rome still sees itself in the tradition of the Roman Empire.
Or alterntively, that it's a relatively modern addition to add to it's mystique for tourism purposes. When did SPQR get added to the manhole covers and does anything else in Rome use similar signage?
The answer is no (and you can easily look this up). SPQR has been used continually since the Roman Empire, through the Middle Ages, by the Fascists and into the modern era by the current administration. You will find it everywhere, even far removed from tourist areas, and there is absolutely no mystique to it. It just means "this is public property of the city". You will also find it on the city's website and on pretty much all symbols of the city. Some of those manhole covers even predate the era of mass tourism... I had one in my yard on the outskirts of the city when I was a kid.