Page number displays on Shabbat

Hi,

One may post individual cards displaying digits in order to show people the proper page number during davening on Shabbat, even though one is thereby "writing" a coherent message in placing the cards side-by-side. This is permitted so long as the cards are not joined to each other.

(Rav Moshe Feinstein, Igrot Moshe Orach Chaim 1:135)

Have a great day,
Mordechai