1. Track badging 2. Enforce RTO via chain-of-command. SVPs, VPs, and directors have aggregate RTO compliance metrics. SVPs crack the whip on VPs to get their numbers up, VPs crack the whip on their directors, and directors crack the whip on their reports, and so on, all the way down.
The actual implementation of the policy was a mess and there was poor messaging especially at the beginning. I'm pretty sure it still doesn't take PTO or illnesses into account — if there's an issue with that, you're supposed to work it out with your manager — and from what I heard they simply handled the holidays by excluding the work weeks before and after Christmas from the metrics. But, ultimately, the chain of command approach appears to have worked very well in terms of actually getting people to come in.
edit: Just noticed from your profile that you also work at Amazon, so I guess there's nothing new in my comment for you :)