It's a pun (?). Denpa literally means "electromagnetic wave" - as in radio wave - but it's also slang for someone who behaves erratically and seems to be listening to voices in their own head (like they're receiving radio messages). Like Koishi. So Utsuho becomes a power plant symbol, and Koishi becomes a radio tower symbol.
Updated
What happened?! You're so noisy! You certainly are a radio-wave person! Denpa-kei (電波系) is a Japanese term for individuals or persons who may feel disconnected or dissociated from the people around them. They may entertain wild fantasies and persecutory delusions or other strong beliefs, and their speech or actions may seem strange or incoherent to outside observers. Radio tower!? And I'm a radio tower, sis!
Power plant!?
I'm a power plant.Okuu turned into a map symbol! Satori-sama, it's a disaster!