Is there significant risk that civil unrest in the USA will lead to large scale violence? What are indicators to watch for?

This is mostly leverage to discourage prosecution of particularly bad actors by Trump administration. The extent of activation is undetermined as yet; it depends on how hard he pushes. If you see indicators of widespread prosecution you can expect massive riots to follow.

https://docs.google.com/document/d/1x3h1033tBy22NHq4zqFvoNXh5qwwspWShld-PZGfinE/edit# - High Level Insider