Apple appears to be taking a harder stance against developers using its custom emoji font, known as Apple Color Emoji, even in the case of apps that have been using the art for years.
Business messaging app Slack used Apple emoji across all platforms until Tuesday, and Facebook's WhatsApp only recently switched to a custom emoji set on Android, according to Emojipedia. Apple is taking some iOS apps to task, rejecting titles from the App Store if they use its emoji in logos, buttons, stickers, and some other forms of content outside of any text entry fields that rely on the native iOS keyboard.
Gray areas include things like notifications, custom emoji keyboards, and non-interactive text. In the latter case, App Store reviewers are said to be inconsistent in their rejections.
While emoji is typically tied to Unicode — meaning that a smiley typed on an iPhone will still appear as a smiley on a Mac, Android phone, or Windows PC — different platforms have different renderings. Apple is turning away iOS apps for breaking trademarks and copyrights.