I think it's more from how each of the fruit on the signs sound really similar to something dirty. Like mango is close to manko, or vagina. Dunno about the first two.
So Yukari, Yuyuko, Kanako, Yuuka, and Eirin have "no experience of men". If I use logic and reason I suppose I could understand but when you consider their age-I mean experiences in life doesn't that seem unusual? We should assist them some how.
Fig
Sounds somewhat like "chinko", the Japanese word for "penis"Mango
Sounds like "manko", the Japanese word for "vagina"Pomegranate
Has the "jaku" that is also in "amanojaku", which means "pervert".