I never worked on an institutional trading desk, but I imagine there must be something akin to "smoke signals" that get sent between players large enough to move the market in order to multiply their market influence without getting accused of collusion. I mean, it wouldn't be hard. E.g. if you see a HUMONGOUS block order on XYZ sector 45 minutes before the open, that's our bogey for the day. The order doesn't have to execute, but it could easily signal all the other players about the strategy for the day.  WallSt Bets on steroids...and nearly impossible to detect.