From The Original Series (or, if you prefer, The Old Show), here are two bumpers that NBC would place to let you know that "tonight's Star Trek will continue in a moment." Bumpers are the names for these little snippets of music and picture to keep you from going to the fridge or the potty.
Related: Some 42 years later, once again, Leonard Nimoy's voice over reminds you the viewer that STAR TREK is coming soon in this, the first theatrical trailer for the 2008 STAR TREK movie. The trailer came out on Friday, the movie is scheduled for December 2008. More at this Trekmovie link.