Various programs display little boxes, if the used font doesn't have a glyph for the character in question. In your case it's the control char \x19 (EM, or "End of Medium").

The regex /^\x19(.*)\x19/s should match, if you match it against a string which holds all the lines, beginning with \x19.

Update: A little clarification as to "How would I match?". If you write my $match = m/.../, the variable $match would hold whether the regex matched. In case you want to extract the part in between the parentheses, you'd have to write my ($match) = m/.../ to provide list context... (as often, context makes Perl behave differently). Also, both matches assume that the string you match against is in $_. If you want to match against another variable (e.g. $text), you'd have to write my ($match) = $text =~ m/.../.