Senatus Populusque Romanus (the Senate and People of Rome). It's a symbol of Rome, the Roman Republic and the Roman Empire. I see it as a purpose in my life to remind people how fundamentally Roman (and Greek, which Rome was a vehicle for) our civilization is. It's a reminder of the fine line between democracy and autocracy, and the vision of universal empire united under providence, as Vergil and Dante envisioned, the ideal Republic and Empire as above so below, both as a model for society, and for the constitution of one's own soul.