No, fascists do use dog whistles. near constantly. In part because they are generally too chicken shit to say anything. It is similar to how (fascist) republicans think they are clever with "go brandon" whereas liberals and leftists just say "Fuck trump, I hope he dies of the most painful cancer imaginable".

And while there are "false positives", those are almost all immediately resolved with "yo dog. Uhm... I get you are in your mid 30s but you may want to stop putting your birth year in posts" and a "... holy fuck. Fucking nazis". Because, "context" generally does apply. The people who need to sign off "14 88" for every single tweet are usually also liking other white supremacist shit. Whereas the people who just got screwed over by what GFWL suggested their username should be twenty years ago have a history of advocating for tolerance and leftist thought.

As for "false negatives": Okay? Some fascists will be undetected with or without acknowledging their "super secret code" of dog whistling.