Rubies by themselves have a number of associations with energy, wealth, power, and love. Rings usually bring to mind weddings, engagements, anniversaries, and are generally associated with couples and vows. Combining these connotations means that a ruby ring can have a lot of meanings. It has also been frequently chosen by kings in portraits, celebrations, coronations, or more mundane use by individuals as an engagement ring.
A lesser-known meaning behind rubies is that they are closely associated with the sun, slightly glowing red from the inside-out due to their fluorescence. There is deeper meaning behind the ring itself too, with the circular shape meant to represent infinity, an everlasting presence. This is a very popular idea for marriage, but it also brings that sense of “forever” to other things like wealth and power. Having wealth and power forever sounds like something a king would want.
The idea of circles and infinity goes beyond rings too. There are other weird and lesser known historic symbols such as Ourobouros, the snake/dragon that forever eats its own tail, which relates infinity in the same fashion. Representation of these symbols might vary, but the circular representation of some type is consistent across the board. A perfectly circular appearance is not always strictly required and can be oval-shaped too, or even box-shaped (frequently used in books), but these can start to detract from the point of the circular shape.
Different jewelry metals like silver and gold have various meanings attached to them too. Gold has been known for its non-corroding properties since antiquity, the yellow color similar to the sun. Much like rubies; gold is considered to be an energizing metal that protects against negative energy, and is another color closely associated with kings, royalty, and the sun again.
Silver is more associated with the moon and “sympathetic” energies, meaning channeling energy into the wearer. There are newer metals like platinum and titanium that do not have historical meanings and symbolism attached to them, but this also makes them representative of new ideas and flexible thinking.