In this intro...

"The Ring-inscription is a Black Speech inscription in Tengwar upon the One Ring, symbolising the Ring's power to control the other Rings of Power."

It's not clear what you mean by symbolising.  How about expressing?

The Ring-inscription is a Black Speech inscription in Tengwar upon the One Ring, expressing the Ring's power to control the other Rings of Power.

What verb you use must describe the noun, "the Ring inscription". Words express meaning. Things like a flag, or a wedding ring, or a letter of the alphabet are symbols.