I have read that Usui instructed the name of the symbol as a sort of mantra to help focus the mind on the energy aspect of the symbol being used.
As fascinator said, "Jumon" I think that is it.
Myself, I think the symbol, and the repeating of the name of the symbol was used (is used) as focusing aid to stay attuned to the "energy" as you use it. However, I also think that using the same symbol with the same jumon, but a different energy would have the same programming/attuning effect if a person was not set onto the energy by use of those focusing "tools" already.
Mantras in meditation are used to focus the mind, or in deity/demon meditation to establish the presence of the being desired; many people believe dieiteis are just energies, and some people perceive them as beings.
Too much thought spoken out, [I've eaten several chocolate nuts today (cocoa beans)}