I haven't seen anything from any of the orbiters yet but here's a shot from Opportunity taken about 3am local Mars time. The comet was at about 400,000kms when this shot was taken.
http://qt.exploratorium.edu/mars/opp...HP2665L1M1.JPG
Here's an image from Curiosity but doesn't look like the comet is visible, perhaps more will be revealed when raw images are available:
https://www.flickr.com/photos/43581439@N08/15554981826/
If anyone's interested there's a thread on UMSF about MER and MSL observations of Siding Spring here:
http://www.unmannedspaceflight.com/i...pic=7866&st=60