A couple of things I wondered about... When Tammy kept changing position/ sending a code, she kept looking at Diane as if she expected a response - but wasn't getting that. That would fit in with Gordon Cole's 'test' of smoking back in the day - and it not being the real Diane.
Also, the lively table message could have been relayed on by Cole (don't ask how the original BadCoop message would have been passed to him, as I have no ideas!) The reason? It was SHOUTED. Maybe she was supposed to recognise it was from Gordon as it was shouty??
Yeah, after all her shifting and staring, Diane shoulda said, "Fuck you, Tammy, what are you looking at!"
Tammy always does that with her hips, though. It may not be a code.
With the smoking scene, I got the impression Gordon came outside because he was craving cigarette smoke. He spends the whole time flickering his gaze between Diane's cigarette and her face with the odd look thrown at Tammy as if asking her permission. Or expecting her disapproval. And his left hand is very fidgety. Diane's body language is far more subtle, but once she notices his interest in her cigarette she gazes steadily into his eyes and I got the impression she was waiting to see how long he could hold out. Then she takes the tiniest puff possible, generating almost no smoke for him to enjoy and he just can't take it anymore and that's when he finally caves... At which point Tammy's dirty looks get a whole lot fiercer.
Yeah, not exactly sure who is tricking who in this scene now. At first I imagined that Cole was trying to bond with Diane through enjoyment to bring her out of obscenity and to the 'dinner table' by reminding her of better times before Mr. C got a hold of her, which was improving Diane's prospects for later in the show, becoming an integral part of Cole's team, etc.; but I guess its still also possible that she is secretly in with Mr. C and is using this as a way to get in with Cole and somehow spy or corrupt them. If she is in with Mr. C, I would find it much more convincing if Mr. C is blackmailing her or giving her a chance at some revenge if she helps him infiltrate/corrupt Cole, FBI et al, or even influencing her to do something that will help Mr. C without her direct knowledge of what is going on and who is influencing her; since, I took her hatred of the FBI and the way she acted during her encounter with Mr. C as genuine and not an act to fool Cole.....(also, I was assuming here that she hates the FBI because it led her to her traumatic encounter with Mr. C); I guess it all depends on if the message she got was from Mr. C and if it was, if she knew it was from Mr. C(still the possibility someone else sent the message, since it was capitalized and punctuated differently)...
Here are a couple of other possible reasons for the text I haven't seen mentioned:
1 - Mr C has never met Diane but he retains some memory of the real Coop and their last encounter. The real Coop would always keep a secret. Diane's secret was so huge that it could destroy her. Mr C's text was simply a threat in an effort to gain some control of her. "the conversation around the dinner table is lively" is simply him taunting her that he knows.
2 - it's an old FBI code that Coop and Diane would use in emergency situations. The fact she's received it will therefore have multiple meanings and she may be wondering if it's genuine or not.