You pretty much have to observe the performance. Well mated means the drones she mated with have different sex alleles from her, so that the majority of the brood survives. You can observe this by a "tight" brood pattern where all the cells are of the same age. A queen that is not well mated (either not enough drones or closely related to the drone) will have a scattershot brood. She can also exhibit a high percentage of drone brood in worker cells.
Its in the way way she walks and the way she talks.
Not sure about what anyone else could say about their observation but the mated swagger is surely different from that of a virgin. Secondly I would say that the "call out" of a piping queen has never been observed in a pile of virgins by this old beek.
As for a "well mated. " This term is an educated guess until she has laid a long while. The "guess" is based on your DCA configuration, Weather, and drone counts at the time of mating....
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