Think about how much time you’ll save not having to pee in a measuring cup before dumping it in a toilet! So much time to gather other metrics about your life
It would be off the waterline of the individual toilet. I imagine the level indicators would need to vary from toilet to toilet because of different toilet bowl shapes.
This could create a bridge between those companies making fly stickers for urinals and the big toilet corporations.
If you want to measure your urine for whatever reason, there are a couple other options. One is you could just time your stream a few times along with total volume. Then you can use time as the surrogate for volume. Another more accurate way would be a precise digital scale. You just need to be weighed before and after, assume a specific gravity based on color, and you’ll have a pretty accurate measurement of volume. But why?