Seems like a credible threat that could be reported to certain 3 -letter agencies to me. But what do I know?It's not like their license plate isn't fully viewable in this picture or anything.
Especially combined with Trump saying "Off to the train station". The "train station" is from the tv show Yellowstone. It's code for where they take people to murder them.
Ask yourself why that would matter to the Secret Service or the FBI who can just run that plate number for all states and territories along with the description of the truck (color, make/model).
I'm also going to say this has probably been posted somewhere else on the internet at higher quality unless op took this photo themselves.
It is utterly tasteless but might not be considered an active threat. They are an edgy clown but there's no indication they will attempt to do anything from that image alone. I'm sure it would make fine evidence in a court case next to, say, guns and maps. But I don't think it can be the basis for a case.
This version also has some darker undertones compared to the Biden one. But they all worship and idolize a rapist so no surprise there.