There are chemicals in the artificial snow at indoor places that will rust edges. Spraying them down with a hose and wiping down the edges with a towel will help and waxing more will help keep the skis in generally better shape. I personally don't use steel wool because it's considerably more abrasive and can cause pitting. Go to a ski shop buy a soft gummy stone. This can usually get the rust off and not take that much edge with it. Also has the added benefit of dulling and smoothing your edges which can help prevent edge cracks.
Hope that helps!