"Instead of seeking many other medicines to cure their illness, I wish people would always honor their own body's healing ability and take good care of themselves."
Meiji Emperor

A symbol is a communication element intended to simply represent or stand for a complex of person, object, group, or idea. It often are graphics or little drawings, which are in fact a comprimed or simplified reproduction of an idea, meant to trigger your consciousness or unconsciousness towards that special meaning. So symbols help us focus and help calling forth a special type of energy.

Do symbols have power? Yes and no.
When symbols are often seen by many people, all these persons at a conscious or subconscious level put their energy in it, connect with it's meaning, and the more often this happens the more powerful a symbol becomes. Thus symbols like the pentagram and the Aum symbol have become really powerful; they have become charged.

On the other hand symbols are just that: a symbolic representation of something. They represent a certain energy, but are not that energy in itself. Reiki symbols are not the Reiki itself, but they help us address a certain aspect of the Reiki energy. Therewith they greatly help us consciously connect to the energy, which highly promotes single mindedness and intent. And if your intent is very clear it gives the universe a clear message of what you want to do or help coming about.

Journey to the red mountain (Tomioka Tessai)

The Reiki energy and the Reiki symbols nurture each other: During an attunement they are given to you, what means placed in your energetic bodies, as a divine sign which says: "you are now empowered by your Inner Flame, to tap into this energy and use it." They are the words of divinity which accompany the divine gift: Reiki. Thus the symbols help one to open up for the gift of Reiki. (So here the symbols 'support' the Reiki.) At the same time the master first opens up to channel the energy through his/her own body and next places the symbols in the aura and chakras of the student. This means that before receiving any symbol by the student it is first charged with the full Reiki stream channeled by the master. (So here the Reiki 'supports' the symbols.) This process explains why a symbol works better/stronger when you are first attuned to it, be it one of the original Usui symbols or any other 'new' Reiki symbol. This explains also why it is very hard to claim that a newly found or channeled Reiki symbol should be 'higher vibrational' than the original ones; they are still charged by that same energy: Reiki, life-force, Source.

Usui gave four symbols for his Reiki Ryoho: one for the physical level, the emotional level, the mental and the spiritual level. Herewith this simple system is complete. With the growing interest in metaphysics, occult knowledge and the channeling of other realms during the last decades, a number of symbols (and additional practices) has been added by Reiki masters. Many of these new symbols are well worth working with, representing a positive energy which can be very subtle. Therefore some of the new symbols are believed to be higher vibrational than the good old Usui symbols, but what you really do is focusing your attention to a very subtle part of the energy spectrum. Still what you channel with these symbols is Reiki, and the base for every new Reiki branch is still Usui Reiki Ryoho. If Reiki speaks to you as a simple, yet powerful and effective system you don't need much to learn for, I would advise you Usui's Reiki. If you enjoy consciously working with various energies, wish to experiment with subtle energies and connect Reiki with other modalities (crystals, chakras, etc.), I advise you to take courses in one of the newer Reiki branches. But you may need to check, because for several new Reiki systems Usui Reiki is a pre-requisite.