By doing a few searches on 'bhcd2' and then 'bhcd' I cobbled together some information from a few sources that may help. First, I noticed that the query string variable 'bhcd2' usually seemed to occur on asp pages.
Digging further, I learned that one thing "bhcd" can stand for is "Browser Hawk Cookie Detector". That's an asp server side add-in that detects cookie content and re-writes it to a query string. And 'bhcd2' could quite likely stand for a second cookie.