chain hanging under bullbar

Hi All,

Just come in from a bit of a trip, and in a few places, I noticed a lot of 4WDs that have a short peice of chain hanging under their bullbars, held by shackles on either side. Looks a bit like a hammock under the front of the vehicle.

But why? I can't quite see what purpose it serves, so if anyone out there knows why, or have done this and can tell me why, I'd love to know.

thanks in advance

TrolUte