letters are meaningless

[-1-]

letters are meaningless. Pronounced as phonemes or written as letters. They only gain meaning etc. etc.

[Walker]

Not entirely. Sound vibrations produce meaningful physical effects independent of any conceptual associations with the sound.

For instance, the distressed whining of an infant can produce repeatable anxiety in its parent.

Premise to consider:
The sound comes first. Later comes the association of sound with a shape such as a letter or a hieroglyphic, or a shape such as a concept. Once the association is established, then the concept-shape can precede the letter-shape and voilà, thinking ensues.

[Eodnhoj7]

letters are meaningless. Pronounced as phonemes or written as letters. They only gain meaning etc. etc.

So that means your statement is meaningless...

[Veritas Aequitas]

letters are meaningless. Pronounced as phonemes or written as letters. They only gain meaning etc. etc.

Yes letters are by themselves meaningless until deliberated by humans and achieving consensus.
This is covered within the Philosophy of Signs.

A sign is an object, quality, event, or entity whose presence or occurrence indicates the probable presence or occurrence of something else.[1] A natural sign bears a causal relation to its object—for instance, thunder is a sign of storm, or medical symptoms signify a disease.

A conventional sign signifies by agreement, as a full stop signifies the end of a sentence; similarly the words and expressions of a language, as well as bodily gestures, can be regarded as signs, expressing particular meanings.

The physical objects most commonly referred to as signs (notices, road signs, etc., collectively known as signage) generally inform or instruct using written text, symbols, pictures or a combination of these.

The philosophical study of signs and symbols is called semiotics; this includes the study of semiosis, which is the way in which signs (in the semiotic sense) operate.
https://en.wikipedia.org/wiki/Sign