search bar

That is a function of the browser which indicates to the user that the page has not been delivered on a https:// secure connection. An https:// is essential for pages where you submit sensitive information, such as payment details, or login information, and such like. On the forum, you will find that should you click 'login', or attempt to make a purchase then the pages will indicate they are 'secure'.

This has always been the case, but recently there has been a push to get all pages on the internet delivered over an https:// connection, and so browsers have made the secure/not secure notification more prominent, thus why people are now noticing it more.

Whilst ProBoards already delivers pages which handle sensitive information on a secure connection, they will be implementing https:// across all pages in the future, most likely inline with the forthcoming version upgrade. In the meantime, however, your members shouldn't be worries by the 'Not Secure', but as with all websites, ensure that they are not submitting sensitive information on pages which aren't secure.