They're made of a distinctively clear quartz glass (used because regular glass is quite effective at blocking UVC), and you can see the filaments at the ends. Hopefully you won't have to ever experience looking at a lit UVC tube, but they appear very different from regular fluorescents.

The comment here has a link to a previous incident of this happening, which shows what UVC tubes look like: https://news.ycombinator.com/item?id=38170902