Ignorance of the law is not an excuse.
This basically means that they can come up with a law, rule or prohibition and not even bother to properly make it public but still punish us for breaking it.
There could easily have been a hidden sign prohibiting what you did.
Ooooh! Now that sounds like fun! Like a demented game of hide and seek, where you spend most of your life looking for hidden signs with hidden laws posted on them, and then at the end, you find one that reads:
It is illegal to look for hidden signs with laws posted on them! ;-)
Actually, actively looking for those signs makes you reasonably suspicious and that is enough for authorities is some places to investigate your activities, question you, or even detain you.
#PoliceState