One way I know it is scouts vs scavenger bees there to clean out the comb frame I've put in, is that once I put a bait box out and it goes plenty of days without seeing any bees at the hive, and then suddenly there are bees going in and out, I know it's likely a swarm will be moving in within a few days. Usually by the next day if I see a lot of scouts. I too have seen them communicating with one another at the entrance. I have also had them scout for a few days and then disappear but most of the time a swarm moves in. It is so much fun to watch the process. Have fun!