If I understood their first demo correctly, they verified a fedora iso with a detached signature. The booted iso then printed "hello 39c3". https://streaming.media.ccc.de/39c3/relive/1854

It was a cleartext signature, not a detached signature.

Edit: even better. It was both. There is a signature type confusion attack going on here. I still didn't watch the entire thing, but it seems that unlike gpg, they do have to specify --cleartext explicitly for Sequoia, so there is no confusion going on that case.