contents - a package object or nil.

 (in-package "CL-USER")  #<PACKAGE "COMMON-LISP-USER">
 (symbol-package 'car)  #<PACKAGE "COMMON-LISP">
 (symbol-package 'bus)  #<PACKAGE "COMMON-LISP-USER">
 (symbol-package :optional)  #<PACKAGE "KEYWORD">
 ;; Gensyms are uninterned, so have no home package.
 (symbol-package (gensym))   NIL
 (make-package 'pk1)  #<PACKAGE "PK1">
 (intern "SAMPLE1" "PK1")   PK1::SAMPLE1, NIL
 (export (find-symbol "SAMPLE1" "PK1") "PK1")   T
 (make-package 'pk2 :use '(pk1))  #<PACKAGE "PK2">
 (find-symbol "SAMPLE1" "PK2")   PK1:SAMPLE1, :INHERITED
 (symbol-package 'pk1::sample1)  #<PACKAGE "PK1">
 (symbol-package 'pk2::sample1)  #<PACKAGE "PK1">
 (symbol-package 'pk1::sample2)  #<PACKAGE "PK1">
 (symbol-package 'pk2::sample2)  #<PACKAGE "PK2">
 ;; The next several forms create a scenario in which a symbol
 ;; is not really uninterned, but is "apparently uninterned",
 ;; and so SYMBOL-PACKAGE still returns NIL.
 (setq s3 'pk1::sample3)   PK1::SAMPLE3
 (import s3 'pk2)   T
 (unintern s3 'pk1)   T
 (symbol-package s3)   NIL
 (eq s3 'pk2::sample3)   T