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The closest you can get in 4chan is using tripcodes. But I'm gonna take advantage of your question to let my inner crypto nerd loose:

For authenticating the author of a piece of text (or for most kinds of data in general), you can use the [OpenPGP protocol][1] for encrypting and signing your messages. The most popular implementation being [GPG][2]. Knowing how to use GPG is out of the scope of my comment, but if you add my [public key][3], you can authenticate that a piece of plaintext was written by me, /u/arian0n, so long as you are absolutely sure that this public key belongs to me, and not to a third party pretending to be me.

I would make this very comment a PGP signed one, but reddit formatting fucks things up a little and it can look pretty ugly.

[1]: https://www.ietf.org/rfc/rfc4880.txt
[2]: https://www.gnupg.org/
[3]: http://hastebin.com/raw/fuwatuniwo
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