"AMD Thunderbird" is a sticker often seen on generic street-market CPU fans. These fans are generally seen on unmarked crappy-looking heatsinks hailing from parts unknown, probably from some small startup Taiwanese company (or maybe from a really big one that's learned never to use its name for anything, lest it acquire a reputation like ECS). The stickers look just like AMD Athlon and AMD Duron stickers, but they're fake while lots of people like to refer to their CPU by core name, companies don't. Do you see Intel calling their Pentium 4s "Intel Northwoods" and "Intel Prescotts"? If you see this sticker on a fan or heatsink, you can be pretty sure it's not actually officially supported by AMD. Probably bad, too.
On a related note, a friend of mine once decided to stick one of these mystery coolers with the AMD Thunderbird sticker on his 1.33GHz Thunderbird-- against my advice, I might add, since bad coolers will cause the Thunderbird to (in purely technical terms) explode, and there's really no way of telling how well these coolers work unless someone's already tested it. The cooler didn't look very good either: bent fins, odd design, mystery fan. It may have been copper, but copper doesn't save a bad design. He stuck a better fan on it, we booted the computer up (also against my advice), and he started a system benchmark to see how hot it ran under full load. About forty-four degrees Celsius. Better than his old (and considerably louder) ThermalTake heatsink.
Despite this positive experience with an Asian Mystery Cooler™, I wouldn't recommend putting anything with an "AMD Thunderbird" sticker on an actual AMD Thunderbird. I may have been wrong in this case, but when it comes to things that may cause your CPU to become a little puddle of silicon and ceramic substrate, it's never a bad idea to judge a book by its cover.