Sign 1 has frame 13 attaching to base 9 and supporting character plates 4. Casing 11 attaches to frame 13 and holds character plates 4 against frame 13. Light assembly 15 and base 9 backlight character plates 4. Backlight is diffusion chamber 17 sidelit by light assembly 15. Casing 11 hides access to the mount and is not easily removable. Light assembly 15 is externally powered and is activated by external messages and by low ambient light. An Emergency Alarm message causes flashing in one colour and intermittent activation of sound. For non-emergency, alternate light mode is used with constant sound. Transmitter 1501 transmits messages for the sign 1. The transmitter 1501 learns emergency telephone numbers for dial detection on a telephone line, in addition to standard emergency telephone number. Emergency button 1507 can begin transmission of emergency alarm message. Transmitter 1501 may have other alarm inputs.