You don't have to embed it into the stream. You just have to show it on start, 10m and the end. So a simple piece of paper with your call sign written on it and placed in front of the camera would suffice. With the RX/TX side, you are supposed to hang or have a label on the remote with your call sign for that.
To your point though, it is unrealistic that someone is going to 1W / 4W (even though they could) the setup. Rather, they will buy the FPVLR (basic or advanced). The advanced one comes with 2.5w boosters - and I am sure most people are just going to slap them on there and go fly. Realistically, they will probably never get caught. Yet, some of the HAMs really like to do foxhunts - but a lot of that seems to have died off in recent years.
Thanks,
-Mike