You've got some great ideas here Carlobrand. I just want to chime in on a few.
I don't deal much with royals, doing of my play in the hinterlands. A ducal signet ring is about as good as it gets out here.
Well, traditional Terran regalia include the crown, orb - representing the world, and scepter/staff/mace, representing might and authority (of the "I thwack you with my stick if you don't do what I say" variety, I suspect, though they became rather fragile for that as they got more fancy).
Orbs usually have a Christian cross on top denoting the sovereignty of God and the church and by inference the divine right of kings.
Scepters aren't just derived from maces but also rods of justice. The may be made of ivory or ash wood, denoting purity and mercy. Actual maces are often presented to cities by their kings to show that certain royal authorities are devolved on them by charter.
Also anything used in the coronation ceremony can be part of the regalia. For example the spoon and holy oil container for kings and queens of England.
Others include: the cape (I've no idea what that's supposed to symbolize); the sword (of war, symbolizing the crown's martial power, and of justice, symbolizing the crown's power to mete out the high justice); spurs (indicating a knighthood, since the king was often chief warrior); the Seal of State. In Japan, one of their items of regalia is a mirror, representing wisdom (through self-reflection,perhaps?). In some equatorial countries, a fly whisk is among the regalia - I don't know what that symbolizes.
The cape is actually ermine. Originally this was the very expensive fur of a little mammal but in heraldry became stylized. It varies across Europe but you can tell things about rank and title from how it is displayed. I remember a certain peer entering the House of Lords during the opening of parliament ceremony in the UK explaining that the ermine he was wearing was bought by his dad in the 30's and he used it because it would be too expensive to replace and he only wore it once a year.
Swords of State are borne before a monarch. In Britain there are five. The jeweled sword used at the coronation, the great sword of state borne before the monarch at the opening of parliament, the sword of justice to spirituality, the sword of justice to temporality and the Curtana or sword of mercy (which is broken and blunt). Each has a meaning denoting the monarch's responsibilities as defender of the faith, kingdom and dispenser of justice.
Seals of State. Also known as sovereign seals. Usually kept by the Chancellor or chief minister or in a republic by the President or senior law officer. To explain it in the simplest way the seal symbolizes the power from which all law in a country is derived. For something to be legal or become law it must be done under the seal. The sovereign seal of Ireland for example comes in the form of a harp. Interestingly it is kept by the President of the Irish Republican Brotherhood, a secret organization responsible for the declaration of the Irish republic.... but thats another story. The President of Ireland and all ministers in the government each have seals of office which they afix to documents to give them the force of law. These seals of office all have at their center a harp identical to the sovereign seal. Each year a "turning of the seal" ceremony takes place to compare the seals of office to the sovereign seal. the seals are offered up to each other to ensure they match. this way everyone knows all laws, documents and licences are legal.
If you are ever brought up in court in Ireland look around the courtroom for a harp. That's an image of the sovereign seal denoting that the proceedings held under it have the force of law. If you don't see it, challenge the judge as to the legality of the hearing. I know the USA and each of its states have sovereign seals, is it possible to do similar there or in the Imperium I wonder?
One more Seal of state story. When Ireland was a separate kingdom with they English king as head of state, that king would send a viceroy to run things day to day. Like England, Ireland had a Great Seal of State that symbolized the King's power. Usually the Lord Chancellor had charge of the seal but in his absence it was kept by the Lord Chief Justices (the most senior judges or legal officers). Several times when disputes arose between the Viceroy and the parliament of Ireland the Lord Chief Justices refused to afix the seal to laws the Viceroy wanted to force through, effectively crippling his power.
Seals are powerful things.
Roman Catholic religious regalia included the flail and crook, harking to more mundane roots and their responsibility to be shepherds of men.
And for the Pope there's the triple tiara, the ring of the fisherman and the stole with the pins in it representing wounds and nails.
Given a far future context, one item of future regalia to consider might be the briefcase, an item containing the codes and communications equipment by which the leader would launch a nuclear attack.
I'll like this idea {steals it}
I think I'd give it an extra twist by implanting the nuclear "football" or its equivalent into the user and as we're talking regalia I'd make it semi-visible maybe the Emperor has a ruby set in his forehead about where the center of a diadem would be. This ruby is actually the IR or laser communicator which gives him access to the Imperial dooms day arsenal :devil:
The British used gorgets, a metal disk hanging below the neck that had evolved from neck armor into something purely decorative - you could restrict that to a certain class of honor-holder.
Most European armies of the 19th century used the gorget and it does indeed come from medieval plate armour. All officers supplied themselves with a gorget, usually of a pattern and metal defined by the higher command or unit the officer belonged to. The practice was for the duty officer or officer of the day at a post to wear his gorget to show he was on duty so that a messanger entering the post could identify him easily. The Germans retained the gorget into the 20th century and certain NCOs wore it. I'm not sure if gorgets are associated with any sign of nobility or noble order but its certainly possible, especially for those serving duty in the Emperor's presence.
Collars (which look like a Mayor's chain of office) are associated with knightly orders. Most have a collar from which the badge of the order is suspended. Some have a star worn on the breast of a coat or uniform, ladies sometimes get a rather ornate ribbon on to which the badge of an order is pinned and worn like a brooch.
In a far future context of ceremonial violence, especially something "grey", you might consider a simple knife or a pistol, communicating a command to do some deed and return with it when you are done. The holder of the knife or wearer of the pistol would be entitled to the full support of the emperor's subjects, but the item would not give command authority - you could present it to the admiral and demand a ship to take you to planet X, but you would not have authority to order the ship to open fire on the planet.
In heraldry a noble's arms (i.e. his shield with the "coat of arms") or banner was given to his agent to show that the agent acted as his proxy.
There's also the marshal's baton, a short ornamented stick denoting supreme authority over military forces.
Sorry for the wall of text.
