Noun 'signals' are the articles a, an, and the that precede a noun. The indefinite articles a and an precede a non-specific noun, signaling that the noun is any of that person, place, or thing. The definite article the precedes a specific noun, signaling a noun is specifically this person, place, or thing. For example:
We saw a robin and an oriole. It wasn't a particular robin or oriole, just any robin or oriole.
We saw the robin and the oriole. These were birds that the speakers are familiar with, perhaps birds seen frequently in their yard or visiting a particular feeder, birds that they have seen and mentioned before.
Signal is a noun (a signal) and a verb (to signal).
It can be used as a verb and a noun
"Noun" is a part of speech that represents a person, place, thing, or idea. It is used to name entities, providing a subject or object in a sentence.
It can be used as a noun or a verb.
The word "core" can function as a noun, adjective, or verb. It is most commonly used as a noun to refer to the central or most essential part of something.
The word hip is used as a noun.
Quadrilateral can be used as a noun and an adjective.
Calico can be used as a noun or an adjective.
Supper is generally used as a noun
Depending on how it is used it can be a noun or a verb.
Reproach can be used as a noun or a verb.
Civilization is typically used as a noun.