inferior-lisp-filter-regexp

inferior-lisp-filter-regexp is a variable defined in `inf-lisp.el'.
Its value is

"\\`\\s *\\(:\\(\\w\\|\\s_\\)\\)?\\s *\\'"

Documentation:
What not to save on inferior Lisp's input history.
Input matching this regexp is not saved on the input history in Inferior Lisp
mode. Default is whitespace followed by 0 or 1 single-letter colon-keyword
(as in :a, :c, etc.)

You can customize this variable.