Starbase 39-Sierra

From Memory Alpha, the free Star Trek reference

Starbase 39-Sierra is a Federation starbase administrated by Starfleet, located near the Romulan Neutral Zone.

While en route to the Neutral Zone to investigate the disapperance of several outposts, Lieutenant La Forge suggests that most of the Enterprise's personnel should be left aboard the starbase to prepare a possibly hostile encounter with Romulan forces. (TNG: "The Neutral Zone")