Reading engraved writings:[1]

Reading writing engraved on a board or pad: Even if the names [of the guests] are engraved on a board or pad and are not written, it is forbidden to be read, as perhaps they will mistakenly come to allow [reading] even laymen documents, as the board and pad are confused with documents.

Reading writings engraved on a wall: However if it is engraved on a wall it is permitted to read it on Shabbos, as the engraving on a wall is not confused with a document. However this only applies if they are engraved concavely, however if they are protruding then it is forbidden even to read them in one’s mind, due to a decree that one may come to erase one of the guests after seeing that he has not prepared for them all their needs, and he will regret that he invited more guests then he is able to [cater for], and he will scrape and remove the protruding names from the wall in order so the servant not read them. This is in contrast to concaved engravings which are difficult to erase, and due to this he will thus remember that it is Shabbos and will not come to erase. Furthermore, even if the protruding engraving is very high up on the head of the wall to which one is unable to reach to erase it, it is forbidden [to be read on Shabbos], because the Sages did not differentiate in their decree between [writing which is]  high  or low, as is written in chapter 275 [Halacha 2[2]]. 

Reading writing written on a wall: It goes without saying that if one wrote with writing [in contrast to engraving] on the head of the wall, it is also forbidden [to read] due to the decree that one may come to read laymen documents, as the writing on a wall gets confused with the writing on a document.

Summary:

On a pad and the like: Just as it is forbidden to read writings, likewise it is forbidden to read words which have been engraved on a pad or board, due to that one may come to read business documents.

On a wall: Words engraved[3] on a wall are permitted to be read. This however is with exception to a list of guests or menu foods which are engraved in the wall in a protruding way as opposed to concaved, in which case it is forbidden to be read by the leader of the household due to a decree that he may come to erase a name.[4]