Guerilla Traffic Strikes

Well, how are they going to catch us exactly?

Much more difficult and more illegal.

Same way they catch people doing any crime: they see you do it, someone reports you, or they get you on camera and most major intersections have cameras on them.

It's a lot easier to avoid getting caught by those methods than if you chain yourself to the road like people in OP's pic.

...

Don't all the police radios have encryption now?

Based.

Hit the bridges that service major shipping ports along the west coast of the US to instantly fuck over the US' side in the trade wars.

After reading this I'm pretty sure that at least a handful of times someone has done this while I was behind them.
It's inscrutable, but I can somehow tell the difference between someone not paying attention and missing a light and someone purposely impeding traffic. There's a cadence.
Another suggestion might be to use stolen or abandoned cars, put fake or boosted license plates on them and park them in the middle of an major intersection. If you park several of them, and maybe interlock them somehow it'd probably be awhile before the intersection became unblocked.

Actually, no. I'm an idiot.

Hit bridges servicing heavy freight rail going to and from american steelyards and go along the east coast to force the US to buy steel from China on China's terms.

Doing it for "propaganda" reasons is retarded and does nothing but annoy people or actively turn them away from what you're saying. Blocking roads isn't a terrible tactic if your intent is directed economic distruption, but if you attempt this without pre-existing support or at the very least significant material public dissatisfaction, then the likelihood of it achieving any kind real significant economic change is slim. By itself, it does nothing to actually force change because it fails to actually coalesce organizational power and offer a prominent challenge to the power of the current state, with it at best causing production to seize for a day or two.
They won't. If they join, it will be because they already had a pre-existing grievance with the current state of society and the material conditions of their situation forced them to take action. People will make decisions based on whether they have something to gain from it and if the ones they are working with or supporting actually have the power or potential power to institute changes that will benefit them. If you both lack support or power and end up being the one who impedes on their immediate personal material well-being, then you will be seen as the problem. To think that people will simply fall in line to support you if you cause distruption is idealistic. They need reasons beyond just PotD to see it within their interest.