Working, tested code:

#!/usr/bin/perl -w
use strict;
use File::Find;
use File::Copy;

# WMA/WMV file signature; See:
#   http://filext.com/detaillist.php?extdetail=WMA
#   http://filext.com/detaillist.php?extdetail=WMV
my $sig = "\x30\x26\xB2\x75\x8E\x66\xCF\x11"
        . "\xA6\xD9\x00\xAA\x00\x62\xCE\x6C";

my @drives = map {$_.':/'} qw( c e );

# Work-around for Win32 bug in File::Find.
chdir $_ foreach @drives;

my @fakes;
find( sub {
  # Skip known NTFS-locked directories.
  $File::Find::prune = 1, return if /^System Volume Information$/;
  return unless m{\.wm[av]$}i and -f $_;
  open IN, $_ or return;
  binmode IN;
  read(IN, my $f16, 16);
  close IN;
  push @fakes, $File::Find::name if $f16 ne $sig;
}, @drives );

foreach (@fakes) {
  print "Fake: $_\n";
  move($_, "$_-fake") or warn "Rename failed: '$_'\n";
}
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