What was the Babylonian/ Akkadian symbol for the god Nebu/ Nabu and
the kings Nebuchadrezzar, Nabonidus and Nabopolassar.

I couldn't find a web image of a pictograph for either the god or the
kings, however I did find some useful information for you.

Nebu or Nabu's symbol is the writing stylus or writing pen:

http://www.bridgesforpeace.com/publications/dispatch/ourjewishroots/Article-11.html

"...The name Nebuchadnezzar, or more accurately Nebuchadrezzar (Jer.
xxi. 2, 7, etc.), is derived from the Jewish Scriptures. But in the
inscriptions it reads Nebo-kudurri-ussur, i.e., "may Nebo protect the
crown"..."

Source:
http://mcadams.posc.mu.edu/txt/ASSYRIA/INSCRB00.HTM

And that last makes it possible to make use of this handy tool for
turning "Nebo-kudurri-ussur" into cuneiform:

http://www.17webplace.com/translit/tranparser.htm

Not exactly what you were after but hopefully it will give you (or
some researcher) a leg up in finding the answer.

Try the University of Chicago Assyrian dictionary, all decent colleges
with a religion department will have one.

morris

About the akkadian symbol for Nebu/Nabo/Nabu/Nebou I found this site,
but it's in French.

http://perso.wanadoo.fr/spqr/pal_dieux.html#Nabo

As I am French, would you like me to translate the few lines about the
God Nebu?

Sophie

You might check here: http://saturn.sron.nl/~jheise/akkadian