I have a signature generator that works and only works with Subsonic Music streamer. Sadly the project looks to have died, it's not been updated in 3-4 years and no longer works on linux. Windows yes, and just about.

I would like a similar signature for Plex Media Server. Plex presents some challenges.
1. Plex can use webhooks
2. It's incredibly secure and cannot be accessed externally unless the server is in a DMZ - VERY INSECURE.
3. It has an ID generator, and on each server restart, this ID changes, so even if you could place the Plex server in a DMZ, you'd have to update this ID
The webhook would have to accept all data from the plex server, then a signature script would have to parse that data into something resembling a signature code.
There may be several styles, immediately I can think of 2 styles.
1. Large and very detailed, with lots of information, EG. Film/song title, starring, rating, and synopsis along with the artwork. Roughly 1024x800
2. 600px wide and 150px high signature, title, year artwork
3. custom text on each style, bottom right corner. This could be username or URL.
Offline:
If nothing is being watched/listened too, then just a brief hello or other custom text to be defined later.
It would be nice if all custom text had a drop-shadow, then it would stand out on all colours.
Plex Webhooks
https://support.plex.tv/articles/115002267687-webhooks/
The backgrounds will need to be semi-transparent, dark and a white pin-stripe around the edges. The BG will also need to have rounded corners, something like this: