Show us the BLM tweet equivalent of "We need to systematically start assassinating Liberal leaders"

well... there's a #killallcops. I'm sure a quick googling could find you plenty more.. : https://twitter.com/hashtag/killallcops?lang=en

Would you consider that hashtag to have serious intent to incite people to commit acts of violence?

The same level of seriousness as any other violence condoning call. In that its hard to gauge intent and willingness to follow through vs. “just saying it”..? where do you draw the line? Do you let one group call for un mitigated violence against a group of people, but not another group, just because you personally dont believe they are serious, even if it might inspire other to take action..?

Yes, context is important. If someone makes a call to violence that is not intended to be taken seriously and is not at risk of being taken seriously that is different from making a call to violence in the hope that someone picks it up at a time when people are likely to act on it.

There is a test for this decided at the supreme court level: inciteful speech can only be prohibited if the speech is "directed to inciting or producing imminent lawless action."

No, it wasn't.