We estimate the prevalence of including political affiliation in one’s public profile among American users of Twitter. In 2020, we estimate that more than 1 in 100 users do so, and that this proportion has consistently increased every year from 2015. By our definition and within our sample, the prevalence of political affiliation surpassed religious affiliation in 2018. Informal expressions of political ideology (e.g. the acronyms BLM and MAGA) followed the same trajectory. We encourage further study of the temporal dynamics of identity through exploration of public profile biography data.