Worth noting that you can both read and print such forms.

That's actually how I checked that I had the syntax right: I wrote:

    (let ((*print-circle* t) (*print-case* :downcase)
      (print '(nodes #1=(a #2=(b #1# #3=(c #2# #3#)) #3#) #2# #3#))
      nil)

Thus proving that reading & printing work well.

Seriously, Lisp is an awesome language.