One may not cut through letters that are written on a cake in frosting, candy, or the like. Similarly, if a cake is decorated with a meaningful picture, like a tree or a house, one may not cut through the picture. Even though one’s intention in cutting the cake is to eat it, since the letters or pictures have meaning and it is very clear that they are being “erased” when the cake is cut, it is rabbinically prohibited (Mordechai; Rema 340:3). However, one may cut between the letters. Even though this separates a word into its component parts, one does not violate Moĥek as long as each letter remains whole. Therefore, if a cake that one plans to serve on Shabbat is being decorated, it should be done in such a way that one will be able to cut between the letters and pictures. Afterward, the slices of cake may be eaten even though eating them will destroy the letters. Since one is engaged in the process of eating, it is not considered Moĥek.
When letters or pictures appear on cookies as a result of having been stamped into the cookie dough, as with petits beurres cookies, there is no prohibition against cutting or breaking them. Since these letters have no significance, erasing them incidentally is not prohibited (MB 340:15).
Some maintain that it is rabbinically prohibited to read a book that has letters stamped or written on the edges of the pages (such as a library stamp) because when one opens the book the letters break apart, and when it is closed they are reconstructed (Levush; MA). In practice, if no other book is available, one may read such a book, because many maintain that bringing the different parts of a letter together is not considered Kotev, nor is separating them considered Moĥek. Additionally, since a book is meant to be opened and closed repeatedly, this is not considered even short-term Kotev and Moĥek, and thus involves no prohibition (Rema 340:3; Taz; MB ad loc. 17).
Some rule that if opening a package of food will definitely tear letters or pictures, it may not be opened on Shabbat. They permit opening the package only if it is possible that the letters or pictures will not be torn in the process (based on Taz). Others maintain that one may open such a package, since all parts of the letters actually remain, but have simply been separated from each other (based on Rema). Le-khatĥila it is proper to be stringent, but when there is no way to open a package without tearing letters, one may be lenient. One who opens the package has no interest in “erasing” the letters, and the action is not constructive but destructive.
One may wear shoes whose soles are stamped with letters or pictures, even though walking in these shoes may leave impressions of these letters or pictures on mud or similar surfaces.
One who wrote on himself with a pen may still wash his hands and dry them in the usual way, since ink generally does not come off as a result of washing and drying one’s hands one time. However, if he would like the letters to come off, he must be careful to wash and dry his hands gently, so that he does not assist in the removal of the letters.