This is the earliest recorded ESB logo, used in a number of print advertisements (example below). It was used in the late 1920s and the 1930s.
The text of the image is transcribed below:
A child can do it!
There is no better argument for Electric Light than its safety.
No other light has the same immunity from danger.
No matches or naked flames.
A child can touch the switch and have light without the possibility of harm.
Besides electricity gives the best light.
Have your home wired and enjoy perfect light and perfect safety.
Electricity Supply Board