By giving blood. I have now given blood on three different continents. They don’t give stickers here though. They did in Spain (well close enough, it was a pin). I did get a packet of iron pills and a bandaid to put on my arm after I took the bandage off.
The process was simple. I showed up was handed an English application after staring at the Thai one for a moment. Grabbed a number and was called a moment later.