Reading descriptions written under designs, portraits and paintings:[1]
A wall or curtain which contains designs of different animals or sketches of people [portraying] historical events, such as the battle of David and Goliath, and it is written under [these portraits] “this is the figure of this animal” and “this is the portrait of this person”, it is forbidden to read this writing on Shabbos due to a decree that one may come to read layman documents. Even to read them in one’s mind without verbalization is forbidden. [See footnote[2]]
Summary:
It is forbidden to read even in one’s mind, without verbalization, the information written under portraits, pictures and the like, due to a decree that one may come to read business documents. [However if the information is engraved on the wall, then it is permitted to be read.[3]]