To get The Revenge of Shinobi and Streets of Rage 2 for free, you need to:
- Visit SEGA's Make War Not Love website and enter your age
- Press the blue "Join the fight" button, sign in through Steam and allow the website to activate CD-Keys on your account, enter your e-mail adress.
Both games will automatically added to your account in 24 hours (Check the DLCs under SEGA Mega Drive and Genesis Classics entry in your Steam library). According to the Steam's store page of the event, there will be more FREE games and DLCs/discounts coupons on selected SEGA releases. Enjoy!