Up until September 1, 2022, Singapore Airlines is giving out 800 miles for signing up to their frequent flyer program, KrisFlyer. You simply need to enter the code
KFFRIEND during the registration process:
This promotion was announced here. You need to enter the code at the end of the form under KrisFlyer registration promotion, and will then get the 800 miles (probably within 4 to 6 weeks):
800 miles are obviously not enough for an award flight, but KrisFlyer is definitely an interesting program and the membership is naturally free. Your miles remain valid for 36 months. You can earn more KrisFlyer miles on almost all Star Alliance flights.