I understood the article to mean, for example, that the help mark allows people on a train to signal "though I may not outwardly appear like I am disabled, I do have a need for priority seating". And thus people would (hopefully) offer up their seat without needing to be asked with words.

I don't think they meant that the symbols should be universally understood without need for explanation. That would be accomplished separately through some sort of public education campaign. In the case of the "help mark", they actually explain what it means in multiple languages in a big sign right above the priority seating [1].

[1] https://www.kotsu.metro.tokyo.jp/eng/guides/conduct/