The keyword term is a noun phrase. Its main part of speech is a noun, with the word "sign" serving as the head noun, or the core component of the phrase. The words "Patriot Day" act as a compound modifier that specifies the type of sign.
In this grammatical construction, "sign" is the head noun that identifies the object. The proper noun "Patriot Day" functions as a compound adjective or, more specifically, a noun adjunct. A noun adjunct is a noun used to modify another noun. The entire three-word phrase operates as a single unit to name a specific item. For example, in the sentence "She purchased a patriot day sign," the phrase functions as the direct object, a grammatical role filled by a noun or noun phrase.
The crucial determination is that the term functions as a noun. While individual words within the phrase can be other parts of speech, their collective role here is to form a specific noun that refers to a tangible or conceptual object. This classification is vital for semantic analysis and content strategy, as it establishes the subject as a specific "thing" rather than an action, description, or abstract concept.
