Cation
This was found at a monkey park on Mt Takao. I stopped and took a picture of it as I was leaving. While I was taking a picture, one of the staff that was in the vicinity asked me why I was taking a picture and was wondering if the English was correct. After telling him the correct spelling, he thanked me humbly. I then noticed that all the signs in the area were brand new and shiny. I am guessing that the staff in the vicinity just finished putting up the sign right before I decided to take a picture of it. 
Anyone remember chemistry?