Early into my search of information on trans people and the way that the world views those outside the norm, I came across this article which I believe is important when speaking about those who aren't cis. It is the duty of cis-gendered mainstream individuals be as informed as possible and not wait for the day someone has to correct us, so this article does a good job of highlighting the importance of not adding an -ed to transgender.

Transgender or Transgendered?