What is the meaning of Watchmen reference?

In the story, we see references to the Watcher. There are a number of interpretations of this usage. First, Oscar refers to himself as the Watcher or a pariguayo, which in Dominican slang refers to someone who stands apart from a group. The pariguayo is always on the outside, looking in. He doesn't seem to belong anywhere; he's the ultimate loner. Here is one definition from the text:

...pariguayos- a word that in contemporary usage describes anybody who stands outside and watches while other people scoop up the girls. The kid who don't dance, who ain't got game, who lets people clown him- he's the pariguayo. If you looked in the Dictionary of Dominican Things...pariguayo would include a wood carving of Oscar.

The word pariguayo was originally used during the US occupation of the Dominican Republic in 1916-1924. Then, US Marines would attend Dominican parties and just watch. Eventually, they were referred to as the Party Watchers. In the story, Oscar is a pariguayo. The narrator, Yunior, tells us that Oscar is overweight (he weighs in at 245 pounds) and can never seem to keep a girlfriend.
Meanwhile, Yunior is a Watcher as well. Although he is more successful at getting girlfriends than Oscar, Yunior is still a pariguayo of sorts. He fails in wooing and keeping Lola, the woman he most wants in his life. On another level, Yunior is a Watcher much like Uatu, who is mentioned in the story. In the Marvel world of comics, Uatu is a member of the Watchers, powerful alien beings who watch and record events across the galaxy. Uatu is important because he has been assigned to watch over Earth. Yunior even makes a reference to the Marvel Comics' Uatu in the novel:

"No matter how far you travel...to whatever reaches of this limitless universe...you will never be... ALONE!" (The Watcher, Fantastic Four #13 May 1963)

So, much like Uatu, Yunior watches over the main characters in the novel, and he provides engaging commentary about their actions. Through Yunior's comments (indirect characterization), the main characters come alive before our very eyes.
Toward the end of the novel, Yunior resigns himself to returning back to the shadows, to the Blue Area of the Moon (where the comic-book Uatu lives). In the end, Yunior is as much a pariguayo as Oscar is; because of his poor choices, Yunior can only observe, not participate, in Lola and her daughter's lives.