Just to emphasize that the Anonymous account seems to be used only in the aftermaths of somebody asking @theymos for him to delete his account, especially in the earlier days, and not, as far as I can see, a feature request that would enable people to posts under an anonymous type of profile (as if most weren’t).

It does not really equate an Alt account. If fact, we can’t see ignored profiles anymore, and all post seem to be assigned to a fake user_id(u)=0 (mouse over the Ignore link of the Anonymous account in the first post here and see the UserId: https://bitcointalk.org/index.php?topic=15911.msg208900#msg208900). It’s also likely  that all Anonymous accounts have their posts assigned to this same 0 user_id, so you can’t tell one from the other apart.