Hi Ashley,
This isn’t a perfect answer, but it is the best I can come up with without a super long investigation.
You can edit /include/staff/login.tpl.php,line 41:
<h3><?php echo Format::htmlchars($msg); ?></h3>
…and replace everything between <h3> and </h3> with your text, like so
<h3>Hello World!</h3>
There are two drawbacks.
If you use any language packs, this will break the translations and your text will display the same in every language.
If and when you upgrade to a newer version of osTicket Awesome you will need to reapply this tweak.