Board Thread:Support Requests - Designing Your Wiki/@comment-33688175-20200317170752/@comment-9605025-20200426021007

That is a warning to let you know that the file doesn't meet certain security standards. I don't know what those standards are but apparently MediaWiki thinks it's worth warning you about. That said, that doesn't necessarily mean the file is bad; it just means MediaWiki can't verify that it isn't bad. As long as you trust the source, you are probably fine.