Mars Orbiter Mission's Mars Colour Camera took a sequence of images of Comet Siding Spring as it passed close to Mars. The five images were taken October 19, 2014 between 17:44 and 18:25 UT, at distances ranging from 180,000 to 130,000 kilometers. The final image was taken at close to the same moment as the comet's closest approach (18:27 UT).
I'm not exactly sure what, if anything, to take away from these photos. They are not of very high quality, but part of the problem seems to be a severe amount of JPEG compression applied to them before posting -- I assume the original data look somewhat better. The original image (posted on Twitter November 12) included caption information describing the top center image as showing a comet jet, but I'm quite dubious of that interpretation -- it looks like stray light to me, an imaging artifact. I post them here mostly in order to complete the set of Mars mission observations of comet Siding Spring! I look forward to future science meetings where scientists will present and discuss all the Mars spacecraft work on the comet.