I have MOCs hashtagged as #moc. Nothing else has that hashtag, so search works, because although “moc” might show up in other notes, “#moc” doesn’t (with the exception of my hashtag index note, which doesn’t present a problem because it’s just one – and it’s kind of a MOC itself, in a way).
I do have one MOC of the highest-level MOCs, but I haven’t used it much.