Actually, in this particular case, it should work with and without quoting, because /@@/ doesn't interpolate anything (as opposed to /@@x/ or /\Q@@x\E/, for example).

#!/usr/bin/perl

use warnings;
use strict;

$_ = 'foo@@bar';
print "matched\n" if /@@/;
print "matched\n" if /\Q@@\E/;
print "matched\n" if /\@\@/;

__END__
matched
matched
matched
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Update: maybe a better (anchored) check, avoiding the potential gotcha of matching against a single-@ pattern:

#!/usr/bin/perl

use warnings;

$_ = '@@';
print "1 matched\n" if /^@@\z/;
print "2 matched\n" if /^\Q@@\E\z/;
print "3 matched\n" if /^\@\@\z/;

print "4 matched\n" if /^\Q@@x\E\z/; # doesn't match, because @x is be
+ing interpolated
print "5 matched\n" if /^@\@x\z/;    # doesn't match, because there is
+ no 'x' in the string

__END__
Possible unintended interpolation of @x in string at ./811585.pl line 
+10.
Name "main::x" used only once: possible typo at ./811585.pl line 10.
1 matched
2 matched
3 matched
[download]