Perhaps Peter Thiel's Antichrist was just looking for her bike...:'p

Same way I can be arrested in Germany for holding up a sign with a swastika. Is it really just “holding up a sign”? Of course not.

There are only a couple of Democracies in the world where you can be arrested on terrorism charges for holding a sign.

I think you just covered both of them.

If you can’t think of words for a sign that would get you arrested in any country you’re not trying hard enough.

A direct threat would do it in most places. You could use the bomb word for example. You could throw in other enhancements as well if you wanted to make sure.

I think it’s important to consider what is on the sign as we render our judgements.

Not the same way.

In Germany, a Nazi swastika is a criminal symbol because Nazism is considered an existential threat since Germany's constitution is built around "defensive democracy", or wehrhafte Demokratie. Consequently, the state is obligated to prevent the re-emergence of Nazism. If you display a Nazi swastika, you will likely be detained for prosecution under § 86a StGB.

There are only a few exceptions (art, science/education, journalism, explicit anti-Nazi protest), but the context has to unambiguous.

This is different from "terrorism law"; instead criminalization of the Nazi swastika is protecting the constitutional order.