In reference to filmmakers who make joking allusion to their other
films, Lucas does this in American Graffiti (a car with a license
plate that reads "THX-1138") and again in Star Wars (a Stormtrooper
whose number is THX-1138).  Spielberg parodies his own
Jaws in the opening of 1941 (and does an homage to Kubrick's Dr.
Strangelove in his casting of Slim Pickens).  And Spielberg plugs
Lucas' Star Wars series in both Poltergeist and E.T. through such
items as the kids' bedsheets and a Yoda Halloween costume.  Some of
this is a variation on "product placement," except they're plugging
their own films (or, in Spielberg's case, those of their friend).
Some may find this self-referentiality either too cutesy or too
self-congratulatory, a sort of narcissistic intertextuality.
It smacks too much of the in-joke (for those in the know) or
advertisements for themselves.    Andrew Gordon