Although the new and old series depicts several versions of Gallifreyan writing (See "The Deadly Assassin", "The Five Doctors", any console screen in the revived series and "Time of the Angels" for examples), English is often displayed purely for the benefit of the viewers.
A prime example of this is in the episode, "The Angels Take Manhattan" in which the Doctor travels back in time to Ancient China and commissions a vase maker include the word "Yowzah!" in Chinese. Once the vase is discovered by Rory, we see the Chinese script rearrange itself to appear as "Yowzah!" in English. The script itself hasn't actually changed, the animation is rather for the benefit of the viewer to see the TARDIS translation circuits in action. Sidenote: because of the linguistic differences and nature of Chinese writing, this mechanism is actually impossible.
Although not as dramatic or overt, we can assume that the words "No More" are actually in Gallifreyan, but appear as English for the benefit for us the viewers. We might also assume that the Doctor has actually been speaking Gallifreyan these past 50 years, but simply heard as English.