I would use Data::UUID to generate a universal unique identifier during object creation; you would store that object identifier and use it later for comparison; in fact there is no reason to compute object fingerprint later.

package Class;

use strict;
use warnings;

use Data::UUID;

sub new {
  my $class = shift;

  my $uuid = Data::UUID->new;

  return bless {
    some => 'data',
    object_signature => $uuid->create_str(),
  }, $class;
}

sub object_signature { shift->{object_signature}; }

1;
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