The present invention relates to a signaling system which provides as part of the signal an indication as to the approximate elapsed time since the activation of the signal. Furthermore, the type of service required can be indicated by a particular flashing scheme or color code. The system has both...http://www.google.com.au/patents/US5800264?utm_source=gb-gplus-sharePatent US5800264 - Method and apparatus for providing a signal indicating the approximate amount of elapsed time 
