Is it permissible on Shabbat to eat or cut foods containing letters, such as crackers that have the company's name imprinted on its surface, or a birthday cake, or does this constitute erasing, which is forbidden on Shabbat?
Most authorities agree that one may bite into and eat a cracker or piece of cake with lettering, even though he thereby "erases" the letters. Since this is done "Derech Achila," as part of the normal manner of eating, no prohibition is violated.
Concerning, however, the question of cutting through lettering on a cake, we find different views among the Halachic authorities. The Mishna Berura (commentary to the Shulchan Aruch by Rabbi Yisrael Meir Kagan, the "Chafetz Chayim," Lithuania, 1835-1933) in Siman 340, Seif Kattan 17, as well as the Chazon Ish (Rabbi Avraham Yeshaya Karelitz, Lithuania-Israel, 1879-1954) in Orach Hayim Siman 61 Seif Kattan 1, ruled stringently and forbade cutting through letters on a cake on Shabbat. However, Chacham Ovadia Yosef in Yabia Omer Helek 4 Siman 38, disagreed and held that this is permissible. He explained that since the lettering on the cake is not permanent, erasing it would constitute only a Rabbinic violation, as the Torah prohibition of erasing on Shabbat applies only to permanent lettering. Furthermore, one erases without the intention to write which is also is only a Rabbinic violation. And in this case, the individual does not intend to erase the letters, but rather to cut the cake. This situation is thus one of a "Peisk Reishei" an action that unintentionally results in a Shabbat violation and, according to Halacha, a "Pesik Reishei" is permissible if the resultant action is forbidden only by force of Rabbinic enactment.
Thus, it is permissible on Shabbat both to eat food that has lettering, and to cut through lettering on food. One who chooses to nevertheless be stringent and refrain from cutting through lettering on Shabbat, in deference to the ruling of the Mishna Berura, is to be commended, but strictly speaking one may be lenient in this regard.