is nofollow default?

[arbee]

I found some old topics relating to this via search but they are years old and possibly inaccurate now.  Does anyone know if, by default, every link posted to the forums / sub-forums are nofollow?  A very old topic claims this as true.  If not, is there an easy way to make specific sub-forums nofollow?  For example on my forum I have a sub-forum called "advertisements" and would like to make that nofollow.