Sigma filed a patent in Japan for a Sigma Macro 50mm f/2.8 EX DG OS HSM lens with image stabilization:
For comparison, this is the lens diagram of the current 50mm F2.8 EX DG Macro lens:
* Patent publication: 2010-271458
* Release date: 12/02/2010
* Filing date: 05/20/2009
* Focal length: 51.50mm
* Fno (aperture): 2.915
* Image circle: 43.260mm
* 3 aspherical elements