I've had a few anonymous comments on Dreamwidth that turn out to be from LJ people I know. You don't have to be anonymous if you're logged in to LJ. Here's what you do.
- Log in to LJ, but then go to a Dreamwidth comment page.
- Pick "OpenID" and enter
exampleusername.livejournal.com(but use your name, silly).
- Write and submit your comment, and LJ asks you to confirm.
- If you say yes, your comment is submitted to Dreamwidth, and I can see who's talking. 8~)