CL-USER> #1=[FOO :bar #1#]
The form read is (FOO :BAR
                  #S(SB-IMPL::SHARP-EQUAL-WRAPPER
                     :LABEL 1
                     :VALUE SB-IMPL::+SHARP-EQUAL-MARKER+))
After initialize instance:
[FOO :bar #S(SB-IMPL::SHARP-EQUAL-WRAPPER..
  [standard-object]

Slots with :INSTANCE allocation:
  BAR                            = #S(SB-IMPL::SHARP-EQUAL-WRAPPER..
#1=[FOO :bar #1#]