While a petition is nice step towards raising awareness, the ultimate decision on what is accepted as a new emoji rests with the Unicode Consortium.
It’s a not-for-profit organisation that standardises letters and characters on computers, a system which is called Unicode. Fundamentally, Unicode ensures that other computers can see each other’s characters, ensuring consistency and avoiding those pesky white boxes you see instead of text.
Unicode is responsible for bringing out new emoji with every version it releases. Unicode 8.0 added the unicorn and thinking face, while Unicode 9.0 featured the addition of bacon and an avocado emoji.