Is this PHP script secure?

I just made a MediaWiki extension for adding banners to the wiki. I set the global variables in the script, which was one of the things that was recommended. Is there anything else I need to do or are there any problems with it?

https://github.com/Sturmkrieg/WikiBanner

EDIT

I'm also working on adding functionality to add a sidebar banner. I made a separate branch with the experimental code. I have a problem where the new sidebar section for the banner displays even though there isn't code in LocalSettings.php telling it to use the sidebar. Seems to be a problem with the if statement and variable.

https://github.com/Sturmkrieg/WikiBanne … Banner.php">https://github.com/Sturmkrieg/WikiBanner/blob/xSidebar/WikiBanner.php