It's good because
1.adds distinction from the user's post (especially if the user always use the [.HR] code)
2.it looks modern (edges are smooth, that inside shadow at the top of the box etc)
It's bad, especially when
1. viewing posts in IB, where users post few words
2. the sigs are aligned left, therefore "adding more weight" on the left side
3. the signature box color is darker than the Username/Status/PostCount/
Rep bar, making the signature box more emphasized.
4. Zoomed out. At some point, like what grav said, it leaves MORE unnecessary space.
Verdict:
NOPE