Looks interesting. Unfortunately doesn't support signing commits - apparently it's possible via "jj export" and using classical git:
https://github.com/martinvonz/jj/issues/58#issuecomment-1247...
https://github.com/martinvonz/jj/issues/58#issuecomment-1247...
There's definitely nothing foundational blocking it though and it will happen one day if you'd like to give it a go in the meantime.