Hehe I know, but I thought it was amusing anyway.
One might say even memories can be erased/rewritten/forgotten as well. Some might even argue that writing something down makes something more real then just being in someone's head, because that way you have a paper trail. Isn't that the whole point of legal identity, to have a paper trail? Isn't that why you are supposed to keep a little piece of paper someone wrote for you when you were born somewhere as safe and secure as possible? Sure it's silly that a little bit of paper is needed to say that you are you, but really no more silly then anything else you could use to prove you are who you say you are. Perhaps the most foolproof method is blood, but of course you are not even using your original body are you?
Also: As for what makes a hashtag fake, I do have an answer: A real hashtag is a feature of a site where something starting with # will turn into a link you can click that lets you search through messages that use the same tag. This site not do this, therefore it's a fake hashtag. But okay, maybe you can just say a hashtag is any bit of text that can be searched like a hashtag. However if you paste #LegalIdentityIsSuperficial into google the only results are from this very page. Therefore it's also completely pointless as a search term and therefore also a fake hashtag. QED.