Well obviously they shouldn't just ram it before even checking, but if someone goes up to it, sees nobody inside, knocks on the window, and nobody responds, they should absolutely have the ability to forcefully, even if it causes damage, move the car.

Whether that's by ramming the tram itself into it (which I assume would require changes to the front for safety against damaging the tram itself) or by using some sort of tool that can push it (e.g. something that hooks onto the rails for grip and uses hydraulics to push the car out of the way), damage is acceptable if you decide your bad parking decisions are justified over every single tram rider's ability to get around, and a ton of money spent to move your car.

At what speeds do you think, a tram, that has stopped and started moving, is going?

The only danger could be to the people standing behind the car, on the sidewalk. But, I think, with enough train horn before the push, it should be safe enough.