A streamer is a vertical line which appears on one side of moving picture image or frame and glides to the other side.  It is used to cue an event:  the start of dialogue, a new scene, a music cue, etc.  When the line has reached its destination, the event occurs.  It may be created electronically in the video signal or etched directly on the work print.  Streamers are used in film score recording, ADR and in mixing.  A series of beeps is also used in ADR recording to indicate the start of the cue.  These beeps may replace or augment the streamer.