I noticed that Shinto priests and old court nobles from the Heian Period (and presumably the Imperial Family now), carry a flat wooden paddle. I think it's called shaku, but can someone confirm that? Better yet, do you know the kanji?
I asked the Japanese staff here and found out that it is indeed called a shaku, written in kanji like this: 笏
Apparently men who were part of the noble family held a shaku in their right hand when they wore formal dress. At first, they would write important things (for example, a program for a ceremony, or 式次第) on a paper and attach it the shaku so that they could look at it and not forget, but later it just become proper ettiquete to carry them around.
Apologies on the very late reply, but thank you so much! I finally figured out what this was on a certain book, but the kanji was still missing. I will be sure to post that on Wikipedia or someplace useful where people can see it.