Here is some research into signs and symbols that are interesting and weirs, I;ve made notes on them and just posted them to my design practice blog because it pertains to how I'm going to use them.
http://thebiggestsecretpict.online.fr/nwo.htm This amazingly hideous looking website does have a rather nice collection of the signs and symbols which I can draw from and put into my book.
http://www.ufodigest.com/news/1106/aliensymbols.html this has a load of allegedly alien symbols which could create a real unique and mysterious quality to my book if I use them well.
http://www.abovetopsecret.com/forum/thread446986/pg1 And here is some more!
Really good links for getting some symbols and imagery, even if they are so incredibly badly designed.