I have no idea. My understanding is it just says "To keep using Reaper past the trial period, you must buy a commercial license" and lets you keep using it with no problems. The official word from Cockos is that they'd rather trust the user to "do the right thing" than to potentially mistakenly punish people who did get a license and have that fail to work for whatever reason (like losing their license file or whatever).
Oh, and the license file is just a PGP-signed chunk of plain text without any real access control or duplication checks or whatever.
Really, it's by far the most ethical, permissive, cooperative, and nice music software activation process I've ever seen.
(Another nice thing about Reaper: At least on the Mac, there's no installer, it's just a single self-contained app bundle. No bloat, no bullshit, no evil pernicious system hooks - it's just a nice, clean, standalone app that makes use of what it can find and doesn't make a mess to clean up later.)