My days as trader date from before the power of the algos. But I saw them being built in my latter years. It was all done by PhD´s and quants, not so much by traders. They often discussed how we would execute trades and orders to implement it in their programs.
When I worked in several Banks, compliance was very much screening everything we did. Everything we said on the phones (it was before electronic trading) was recorded. They listened to our conversations without us even knowing. In the later years we were prompted by our managers not to use mobile phones on the trading floor (to eliminate the risk that people would signal someone outside when a big order would go trough). In such a spirit, I would myself not find it appropriate for the above reason to participate in "retail" discussion boards and I never did.
You may remember that several bank traders in London were fined for using private chat-boards to discuss and exchange FX fixing orders. They were calling themselves "The Cartel" . I think you can find some stuff still on the internet about it, they and their employing banks were fined heavily .
As for gauging market interest or market flavor, we as traders would often walk over to the different sales desks and ask what the real money clients were thinking/ doing, what the retail clients (leveraged players) where doing "on balance". Big orders were written on a board . This gave is some inclinations how the market was structured and what we could expect. Real money does not "cover" their positions quickly, they are often permanent flows staying in the market. Leveraged players were pure speculates and have to bail out at some stage. We would find out where their stops are etc. This would all be digested now by algos.
