Yes there is!
If it's PHPBB3, it's as simple as a part of the control panel where you make BBcode.
If memory serves me correct,
Admin Panel > Posting > Create new BBCode
BBCode Usage
HTML Replacement
And check "display on posting page".
If it's PHPBB2 you've got to install the custom BBCodes mod -which should take you a good hour - and then follow up in the posting templates for each skin for each BBCode you've made up. It's not brain surgery.
Strikeout code once again is
i've ran quite a few forums in my time - hell, I even used Getaway Blue, too so enjoy stuff ok
If you've got the gusto you can even write a SPOILER tag too, which would be very helpful. Making custom BBCodes in phpBB3 only requires HTML knowledge.