Venus has a general retrograde wind direction, and a few days of measurements from the InSight lander so far suggest steady winds from the north-west, but are there any measurements that indicate Mars has a general, prevailing, or predominant wind direction? Maybe observations of clouds, or doppler radar somehow?
An annotated image of the surface of Mars, taken by the HiRISE camera on NASA’s Mars Reconnaissance Orbiter (MRO) on May 30, 2014. The contrast has been enhanced in this image to better show the region where InSight landed on Nov. 26, 2018. The labels show the approximate position of NASA’s InSight lander in Elysium Planitia. Overlaid on top are the direction of the vibrations detected by InSight’s science instruments. The diagonal lines, faintly seen moving from upper left corner to the lower right corner of the image, show the paths of dust devils on the Martian surface. The vibrations recorded by InSight line up with the direction of the dust devil motion.
Direction of dust devils isn't necessarily a slam-dunk for the direction of a "prevailing wind" but it might be suggestive.