Old Shoe

I'm reading some of the fascinating case studies on the High Scalability site, and I stumble across this curious bullet point in the page on Amazon's architecture:

"Don't pay for performance. Give good perks and high pay, but keep it flat. Recognize exceptional work in other ways. Merit pay sounds good but is almost impossible to do fairly in large organizations. Use non-monetary awards, like an old shoe. It's a way of saying thank you, somebody cared."

Emphasis mine. What on earth does this mean? Is it some phrase or saying I'm not familiar with? Surely Amazon don't literally hand out old shoes to their best techies...?

Updated - OK, I just Googled and found some citations confirming that, yes indeed, Jeff Bezos did hand out stinky tennis shoes to Amazon's high-achievers:

How bizarre...