That used to be an unofficial convention of the Spanish language regarding accented letters: only in minuscule text but not on majuscule (capital) text. The Royal Academy has always supported (since at least 1792) that majuscules should be accented, but it was difficult to do so since movable types and typewriters didn't allow room for them: https://upload.wikimedia.org/wikipedia/commons/8/82/Acento_e...