Bing is adding reminders in their search results when you have previously visited a webpage.  This is similar to a feature Google has, which most often appears to users using Google Now.

This type of feature always has mixed results, as some people find it useful, while others find it on the creepy side, since it does make it obvious that the search engine is keeping track of what sites the user is visiting.  The link to search history is a nice addition though.

This appears to be a limited test at this time, so it is unknown if this feature will ever go out to all users.  This was the only result I saw that had this notation, despite doing multiple searches with sites I had previously visited displayed in the results.