Seems simpler?
Also, side note, I’ve never seen the glass anything other than full.
The glass only appears on the (vastly more expensive) pub licensed feed, not on the consumer feed. The higher cost and much smaller pool of licensed customers reduces the likelihood of someone pirating the feed and vastly simplifies the process of identifying the leak. A pirate could burn in the right logo to a standard consumer feed, but they'd need daily information from someone who can view the pub licensed feed.
Given the incredibly devious history of satellite anti-piracy technology, I would fully expect Sky to have a bunch of other, subtler data hidden in the feeds and codecs.
If you're playing live sports in The Temeraire, and The Temeraire doesn't have a license, then boom. You're knicked. Pubs are licensed and not readily movable things owned by specific (and licensed) people. Walk in the door, if they are playing sports and this pub is not registered then you know right away. You'd in fact only target pubs that dont have a license. No need for any steganography.
Of course you might want it if someone is streaming this sports feed from a pub licensed feed to the internet, but then why have the global changing beer glass?
The glass provides an instant clue for inspectors, but also the general public. A busybody (or a rival publican) can instantly spot if a pub is using a dodgy satellite feed.
There's also the underlying tension between Sky Television and the English Premier League, who both have slightly different incentives around rights enforcement. The pint glass allows Sky to easily audit pub landlords, but it also allows the Premier League to audit Sky.
It's not a comprehensive anti-piracy system in itself, but it's a really useful and really simple tool.
https://helpforum.sky.com/t5/How-to/What-s-that-9-digit-numb...
Pub streams are also probably harder to pirate. You might get a single stream license and use it in the 3 bars you own, but then the service provider would quickly wonder how comes you own 3 sports bars and have a single license.
The satellite feed that's licensed for public venues has a small beer glass logo burned in to the image. The amount of beer in the glass changes every day on a pseudorandom basis. An inspector can check whether a pub has the right license simply by looking at the screen - if the glass is missing or contains the wrong amount of beer, it's an unlicensed stream. It's plausibly hackable by a sufficiently motivated person, but it's a remarkably simple and effective deterrent.
https://mindyourdecisions.com/blog/2016/12/13/game-theory-ap...