I tried to have hints/indicators for all of the hidden signs. There might be a few that I didn't do a great job with. For example, the level 2 hidden sign used to be MUCH harder to get, involving extremely precise wall jumping that wasn't even obvious in the first place (you still can get the sign this way, but I'm guessing most people don't). I added the 'hidden block' way to get it as a result, which, to be fair, isn't super intuitive. I think my thought process for that was to have a small area that seemed empty/pointless, thus it made sense to test the walls for potential secrets.
That mechanic can be dangerous though, because I didn't want to create a game that just had a bunch of random false walls or invisible blocks that you need to find, because that can get tedious and frustrating, so I tried to avoid that as much as possible.
Glad you like the game, and thanks for the comment! :)