I understand where you are coming from Yurisenpai :3 but at the same time I wouldn't look too deep into Botan's hand gestures. If the gesture you saw truly is a gang sign of some kind it could very easily have been put there unknowingly. As I said before as an artist, when I draw, I draw what looks appealing. I could see someone drawing Botan for the anime and moving her hand in that position because it looked comical or the position set off a style or flair to accent the scene/moment.
That or sure perhaps it is a known gang sign in Japan and an animator thought it would be funny to add it in as a joke. Either way, whatever the reason, I really wouldn't worry too much about it. In fact, I will be honest, now I am imaging Botan as a gangster and that just makes me giggle. I can see her wearing a pink beanie and an oversized pink and purple hoodie with Hello Kitty glasses. ...I may have to doodle this now. xD <3
As for maze castle, that is a good question. I never thought of that before! Knowing Hiei and Kurama though, it would be all too easy for them to get through the castle. Hiei's a thief and Kurama was a spirit fox who specialized in codes and thievery and such so...I think breaking out of the castle would have been a cake walk for the two of them. ;3 I wish that scene had been in the show! cool