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According to this answer the weather at the InSight lander on Mars can now be seen online at https://mars.nasa.gov/insight/weather/ This includes the wind speed and I believe the direction (if that's what those little flags mean).

Question: But I'm not sure so I'd like to ask; what do the little flags on these martian wind speed data points mean?

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A bit of history...

From the question Was the telltale on the Mars Phoenix Lander used for meteorology? Why not a hot wire anemometer instead?

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above: GIF from images transmitted from Mars. From the The Telltale project page on the Mars Simulation Laboratory. Also archived here.

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They indicate wind direction (given by the long line or "barb") and speed (given by the shorter flags extending from each barb). In the same linked page you can read:

The barbs extending from each wind speed data point indicate the compass direction of the wind (e.g., a wind blowing from the north will have a barb straight up above the point; a wind blowing from the west will have a barb off to the left). Full and half flags extending from the barbs indicate the wind speed, with each half flag representing approximately 2.5 meters per second. A circle in place of a barb indicates a wind speed less than 2.5 meters per second.

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  • $\begingroup$ Thanks for the speedy answer! I am remiss for not noticing it was on the page already. I wonder if there is any utility to modulating the barb size on data points that already indicate the wind speed, or if it's done simply because it's standard. Also wondering if 2.5 m/s per half-barb is standard, or if these chars always need a half-barb scale explanation. Do you think those need a separate question? $\endgroup$
    – uhoh
    Commented Feb 24, 2019 at 0:56
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    $\begingroup$ Yes the flags are redundant in a speed plot, but as you say it is used because it is standard in meteorograms (barbs that include flags). The flags also make a bit more intuitive to figure out the direction the barb is pointing to. The speed of 2.5 m/s per flag is not standard (at least not in the NOAA GFS meteorograms that I often use). $\endgroup$
    – Camilo Rada
    Commented Feb 24, 2019 at 1:05
  • $\begingroup$ the directional arrows and flags are a standard for most meteorological services around the world. $\endgroup$
    – trond hansen
    Commented Aug 28, 2019 at 21:06

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