I agree that this can be a confusing case. I'm going to have to agree with Lee, and I'll explain why in a moment here. Yes, due to how the commas have been used, this can look like a mess and confuse us as to which noun is being referenced. However, we'll have to take another look and see that, from the get-go, "hardcore graffiti" is the subject of this excerpt. Additionally, if we look at the words contained in the parentheses, they're being used to describe hardcore graffiti and you can see this by the singular possessive "its" which means it cannot (at least not without being grammatically incorrect) be referencing the plural "taggers" or "writers" or "sprayers". Another reason why this is confusing is because immediately the writer switches to speaking of the possession of the graffiti by the "taggers, writers or sprayers" and we can see this by the use of the word "their" which is third person possessive plural. Yes, we might hear (especially when the gender is unknown and one wants to avoid being offensive by using "its" which is typical with pets) someone refer to something possessed by the subject as theirs and in my case where theirs would be correct. However hardcore graffiti, being impersonal should not be referred to by "their". Furthermore, as we continue in the sentence the writer again immediately switches subjects they're speaking about and again references the graffiti saying "is not" which is referencing, again, the singular. We can also see the writer is not referring to the artists here as artists can not be used to gain respect of fellow artists, but art can. I apologize if this took a while and I hope I've explained thoroughly and cleared up any confusions there might be.

To me it seems like it's referring to the "taggers, writers, or sprayers". They aren't known outside of their community, but they know of each other, so it follows that they're seeking recognition from each other rather than the community at large.

The meaning of the graffiti is known only to the community of taggers, writers, and sprayers.