That will insert "BVB: <userid>" into every post's text (BVB = "Being Viewed By"). That text will be the same color as the post background and not viewable unless the text is highlighted using your mouse. I'm guessing the site is copying all text, no matter what color it is, so that would be copied too.
If you actually want the BVB to be visible on your site just use this code..
Ok tried the first one, not quite working. It is displaying a visible code on the screen but not showing the userid even after highlighting. Posted screen capture below.