The most common type of street crossing sign for assisting the visually impaired employs an audible signal to indicate when it is safe to cross the street.  While the sound employed by the audible signal may vary, the typical sound is a simulated bird sound, with a different bird sound representing a different direction in which to cross.  The audible systems are typically associated with existing street crossing signs and are designed so that the tone emanates from the area of the walk indicator when the walk indicator is activated. 
However, in order to be heard over the noise of the traffic at an intersection, the sounds must be of a substantive volume.  The audible signals typically employ feedback systems so that the emitted sound is a predetermined level above the ambient noise level.  This increased volume is extremely distracting to drivers, and also makes it difficult to hear sirens from emergency vehicles.  In addition, the audible signals can be bothersome to local residents and businesses proximal to the signal. 
The audible signals have another disadvantage in that these signals call attention to the users of the signal and identify them as visually impaired.  As many of the visually impaired are highly self sufficient, they do not wish to draw attention to themselves and desire a discrete street crossing system which can be used without attracting undue attention. 
In addition, the audible signal crossing aids do not provide additional information which is helpful to the pedestrian, such as the distance between curbs and/or the number of lanes to be crossed, the name of the streets at the particular crossing, or the presence of hazards in the intersection, such as construction barriers or islands. 
The prior attempts to provide a suitable street crossing aid for the visually impaired have included the U.S. Pat.  No.  4,570,474 issued to Patterson, entitled "Street Crossing Signal Device for Blind Persons."  The Patterson device comprises a pair of rigid hand rails secured to a post at the corner of the intersection, such that each hand rail has a portion oriented in the direction of a corresponding crosswalk.  The device further includes a vibrator means disposed within each hand rail, which vibrates when the traffic lights permit crossing in the direction of the rail. 
However, as each hand rail extends from the post, the rail represents a substantial obstruction to the flow of pedestrian traffic.  Pedestrians are forced to navigate around each hand rail in order to pass the post.  Further, the addition of hand rails to existing sign posts represents a time-consuming, labor-intensive, and therefore expensive process. 
Therefore, a need exists of a street crossing signal for the visually impaired which is readily adapted to existing crossing technology and does not draw undue attention to those who use the signal.  The need also exists for a street-crossing signal for the visually impaired which provides additional information such as the name of the street to be crossed, the direction to walk, the distance between curbs and a silent indication of when it is safe to cross, i.e., when the walk interval occurs.