Yes, one of the ways that investors, or traders asertain a likely Bearish scenario is when a big supply is entering into the market. To know if there are huge supply coming into the market can be through news channels and social networks.
For example, when the Germans government wants to sale off some of it's ceased Bitcoin, the were some information on social networks that ignited Investors/traders the awareness, and everyone were monitoring the situation closely.
Again, when MtGox exchange decided to pay it's users after the hackers incident, there were also information that alerted investors/traders etc.