Twitter announced that it is introducing QR codes to make it easier to follow users.
The idea being you can add the code to documentation, business cards, publicity material, etc., and users simply scan the code and you now have a new follower.
It's being tested and and some users can see the "QR code" option.
There's no information right now as to when it'll be rolled out to all users.
...announce the launch of QR codes on twitter! they work like snap codes! find yours: profile > gear > QR code Twitter Announces QR Codes [twitter.com]