The keyword term "sep 11 logo" functions grammatically as a noun phrase. The main point and the core part of speech within this phrase is the noun "logo".
In this construction, "logo" serves as the head noun, identifying the subject as a specific emblem or symbol. The preceding term, "sep 11," is a proper noun (representing the date September 11th) that functions as a noun adjunct or attributive noun. A noun adjunct is a noun used to modify another noun, operating in a capacity similar to an adjective. It specifies the type, purpose, or context of the head noun. Therefore, "sep 11" defines the specific category or theme of the logo being discussed.
For the purpose of an article, this grammatical structure dictates that the central focus must be on the logo itself. The article's subject is not the event of September 11th in general, but rather a tangible or conceptual logo associated with it. The primary discussion should revolve around the logo's design, symbolism, history, usage, or impact, with the "sep 11" context providing the essential framework and significance for that analysis.