That is an old trick, commonly shared or reinvented. It’s hit or miss. Usually it’s close enough you don’t notice, but some people realize something is wrong and have to readjust. Also it’s more of a one off thing. Sliding the post past the line has a habit of removing bits of the line, or obscuring it if you used a little too much grease. Not often but I have seen someone lose the line entirely by fucking around. If you were using it daily you’d get the same effect quickly enough.
Once you are really, really certain you have dialed in the right post height, I’ve known a person or two to use a scribe line. I was never that brave. Another just used electricians tape which might fit depending on how this system works.
The sticker/tape solution means you've made the choice to remove the seat post entirely when you move the seat. Since seat posts historically have been greased (to prevent galvanic action between the aluminum seat post and the steel/titanium/?? frame), that can get messy.
Most people, when they stuff their bike into their car, drop the seat post all the way into the seat tube, rather than removing it, and that can peel a sticker off (worst case, inside the seat tube).
On the way to a trip these things are trivial, but at the end of a trip, every little problem is much more likely to get on your last nerve, so finding solutions that take care of future you is a useful investment of problem solving. If it's raining and you're covered with road rash you don't want to deal with your greasy seat post for the 35th time on top of it all.
This bike is designed around removing the seat post so I wouldn't apply rules for other bikes here.
Anecdotally, I have never dropped my seat post even when stuffing a bike in the trunk and neither have my riding partners and a lot of us have carbon seat posts now so we don't grease them. Most of us are simply too iffy to mess with our riding configuration. I'm also sure professional bike fitters wouldn't use a solution that would inconvenience most of their customers. This urban frame lock bike is a very special case and should be treated as such.
Once you are really, really certain you have dialed in the right post height, I’ve known a person or two to use a scribe line. I was never that brave. Another just used electricians tape which might fit depending on how this system works.