Prepending character(s) to a custom <!--more--> tag title?

I'm hacking around with a blog using Cordobo Green Park and I've noticed when I specify a custom title, instead of it beginning with a » symbol (as it does for the standard "» Read more: [POSTTITLE]") the custom message is simply shown without any prepended character. It's a shame, because the » character would be nice to include for visual consistency.

In ./themes/cordobo/index.php (lines 28-30) there's this piece of code which I think handles the tag:

div class="entry"
   ?php the_content((__( 'raquo; Read more: ', 'default')) . the_title('', '', false)); ?
/div

Which differs from the Codex example with no 'default' second variable:

?php the_content("Continue reading " . the_title('', '', false)); ?

Never mind my puzzlement over the __( after the initial double opening brackets (the Codex doesn't really have anything of help to me for explaining this - any takers?) ... I just can't figure out how to simply prepend the » character to custom !--more-- text.

I'm just tying myself in knots here, but I think the actual crux of adding a prepended character(s) to custom titles is modifying the action of the regex-detecting-then-variable-setting function of get_the_content inside post-template.php (line 203):

$more_link_text = strip_tags(wp_kses_no_null(trim($matches[1])));

However, what's the best (non-destructive, and upgrade-proof) way to override the default behaviour of that subroutine and define a customised version of $more_link_text? I really don't want to go destructively hacking core files, but I struggle with coding filters so at the moment it's still looking tempting.