Yes I've seen them.
That was in Empire you only would see it in campaign battles it means you can put a unit of men in the building.
The Star seems to do this when a unit is effected by a Generals abilities rally or inspire.
I think but I'm not so sure that these is the unit getting experience.
I could be wrong but that seemed to me to be what was going on when I've seen them.
Hope that helps some.
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