Maybe useful for others as well or maybe there is already something like this, i dont know.
I didnt had a chance to test this in real games so far, so it is BETA. Any bug reports or improvement ideas are very welcome.
One idea is to use different colors for different teammates. At the moment all selection circles are just green regardless of the player who selected that unit.
BTW: This only works for teammates who have this widget too!

v2.0
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-optimized sending
-debug mode disabled
v1.9
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-ally units triangle changed to pentagon
-fixed: markers appearing behind terrain/in front of units
-marker now not ground only: airplanes fixed
Updated 1.85:
-Zlib compression added
-small improvements
UPDATE 1.1:
-improved network load
-different colors for each teammate
Download in SpringDownloader or at
http://www.springinfo.info/index.php?page_id=690#136