The introduction of emoji skin tone modifiers to the Unicode Standard in 2015 was met with considerable debate on the extent to which these emoji would be used, who would actually use them, and what they would actually be used for. I evaluate such claims against large datasets drawn from social media and find evidence that people generally produce skin-toned emoji which align with their real-world identity. I also identify particular variations in emoji production based on real-life skin tone and geographical location, as well as the context in which emoji are used. I test experimentally the extent to which people perceive identity from the emoji that others produce, finding that these emoji are strongly considered to represent specific identities for both authors and readers of social media. Even default yellow emoji without a skin tone are associated with a particular identity. The ability of emoji to index identity for both author and reader is a property found in language, where one consequence of this is a difference in attitudes, responses or behaviours towards perceived identities. Whether the indexicality of emoji can similarly affect behavioural outcomes is tested experimentally, where no such effect is found.