I had classes like that, where at the beginning of the quarter, each student gets assigned an username of the form "<course id> <three alpha characters>" and al

I had classes like that, where at the beginning of the quarter, each student gets assigned an username of the form "<course id> <three alpha characters>" and all participation is based on username from then on. Even though the usernames are seemingly random, certain usernames started gaining reputations on the class discussion forums, and students come to recognize some names. But computer science courses tend to have very objective rubrics for grading, so I am not sure the anonymity mattered much.