The Ring of Rassilon is of course an essential accessory for anyone wishing to make it in the dangerous world of Gallifreyan politics. With it, you can show your Prydonian affiliations, seal your letters with the Wax Seal of Rassilon, and even mark your enemies with it if the council meetings get a bit raucous*.
To fulfil the general function of creating wax seals, the Ring of Rassilon is quite big, and should fit around most fingers fairly loosely.