In the UK, the standard was BS3939, Graphical symbols for electrical power, telecommunications and electronics diagrams.
British Standards can be ordered from http://bsonline.techindex.co.uk/

I believe that BS3939 has now been superseded by a European standard; not sure of the number, but could be EN60617
http://www.cenelec.org.

See Also IEC 617. (Possibly now IEC60617?)
http://www.iec.ch/
There are some course notes at:
http://courseweb.chchpoly.ac.nz:8081/eis/units...c_617d.htm

No Doubt ANSI also has something to say on the matter!

Many large companies also had their own internal standards - maybe they still do?