All right, this won't probably be too sophisticated neither very imaginative, but I needed something unusual to put in my signature on another board, so, here goes:

my $country = "'tis of thee";
sub sing;
sing ("sweet land of liberty")
    if $country =~ m/^'\w{3}\s\w{2}\s\w{4}$/;
[download]

The pattern is, of course, a little obvious but I couldn't come up with anything better at the moment I wrote this ;-).