Kazuya Sakakihara spent ten years working at Sony as a senior software engineer, helping bring both the PS3 and PS4 to the world. He's no longer at the company (parting ways in early 2013), but before he left he made sure his name quite literally lives on inside the code of pretty much every PlayStation 4.
As you can see here, in this snippet sent in by Chris Gallizzi, Sakakihara has left his name inside the PS4's HDD code. Now, coders leaving "calling cards" is nothing new, it happens all the time, but it's usually left in the "comments", the parts where humans leave human messages for other humans. And even then, it's often in the form of initials. Sakakihara's full name is lying there in the actual code, and doesn't require any kind of decryption to see it.
Sure beats scrawling it on the bathroom wall on his last day at the office.
Interestingly, his name also has a typo. I wonder if that was just that, a typo, or whether it was a concession to keep the code humming.