Google UnSafeSearch and Yahoo UnSafeSearch are ways billed to find content that both search engines DO NOT consider safe for family-friendly viewing. They work by doing a search with filtering options at both search engines switched on and off. It then compares the results and shows you whatever was being filtered out. The result is to give you only stuff deemed "unsafe." Unsafe Search Results is a similar service.
Why might you use these other than to find unsafe content? I came across them via Tara over at ResearchBuzz, who notes in Unsafe Searching on Google that this can be a way to see if the filters are slipping, censoring content that might not really be unsafe.
She suggests trying a site search for your own site, to see all your pages that might be accidentally filtered, such as some of these pages in a check on Amnesty International. The only problem is, you won't be shown all your pages. You'll only be shown all the pages from the first 100 results that are checked. You could have more pages being filtered, if you were able to drill deeper.
Need to know more about enabling such filters if you want them, bearing in mind that they aren't perfect? Our Kids Search Engines page has tips and information.