On this question discussing whether a Jew may participate in the Biblical Hermeneutics Stack Exchange site, one of the issues raised is marit ayin. But does marit ayin really apply on an anonymous internet site? Should a Jew be worried that others might think that he is doing something wrong, even though nobody actually knows who he really is? After all, for all anybody else knows, the person could even just be pretending to be Jewish.
Halachipedia (link) cites Mesechtas Shabbos 64b and Tosfas Mesechtas Kesubos 60a as saying that marit ayin applies even in private, but possibly only for d'oraisa:
The question becomes: Does participating in the Biblical Hermeneutics Stack Exchange look like something that is asur d'oraisa (while being technically permitted), and why would it look forbidden?