The Serenity is regularly involved in activities of dubious legality, and is often on the run from either the authorities or powerful criminals and mobsters.
In the meanwhile, Inara, a companion, travels with them, communicates regularly with her guild, asks them information on potential clients on the planets they visit and arranges trades with them.
So it seems to me that someone powerful enough (or connected enough, or with enough hacking abilities) could infer the position of the spaceship by monitoring her activity. Isn't this a problem? Why does no one worries about the fact that their "ambassador" might make their position known to their enemies?