Something that popped into my head today, when Obi-Wan and Yoda sneak back into the Jedi Temple after Order 66, did he record a message in his voice, or just a general warning to stay away from the temple and go into hiding? I don't think I've ever seen anything that tells exactly what the message was beyond that or if it included any other info. You'd think he would have it say to go into hiding and that the Sith are in control. Most of the old EU had characters find out about the Sith, but apparently not from that. I don't remember if even the Rebels characters knew about the Sith until they encountered Vader. Obviosly Ahsoka sensed that it was Anakin, so she knew, but I'm guessing that info wasn't broadcast with his signal.