Yes, that's all. It has no other meaning. If you do a search for that tripcode, you find articles and tweets where Q is cited. This is why there's a lot of interesting stuff appearing. Another reason is for the Google books or Amazon search results. They follow the rule: Who else searched for this word(s) and in what was he interested. So you'll find a lot of books other Q followers looked for. This means that the "!!mG7VJxZNCI" has no secret meaning but works as a common tag for search engines. It's not intended but can be a means to find interesting discussions and articles from other Q followers.