絵馬 - Wishing Plaques
A common sight in Japanese shrines is walls of 絵馬 (えま) , or wooden wishing plaques. Remember that shrines (神社) = Shinto and temples (寺) = Buddhism, so the tradition of 絵馬 is Shinto. However, because the two religions have blended so much, you can now find these plaques at temples as well.
Obviously, there are two kanji in the word 絵馬. One means picture, while the other means horse. This is because horses were seen as messengers to heaven. Some people donated horses to shrines to have the gods hear their wishes. However, if you haven’t noticed, horses are a bit pricey. The tradition morphed into donating figures of horses, and then these plaques with pictures of horses. Nowadays, plaques aren’t always of horses. It’s very common for the zodiac of the year to be on plaques, the shrine’s emblem, or other religious art. Often times, these designs are localized to the shrine selling them. For example if a region is famous for a particular legend, the 絵馬 will have a picture representing that. Sometimes there’s even plaques with pictures of anime characters!
Basically, these wooden plates are meant to write messages and wishes to the gods on. These wishes can be for good luck on exams, safe childbirth, love, general happiness, anything the wisher wants really. Shrines sell the plaques for people to write their messages on. The money then goes back to support the shrine.