Some time in 2015, we shut down sh.sg to the public because spam bots were the main "users" of the service. This was rampant even after we introduce a Google captcha. We could have tried increasing the complexity of the captchas but that's not going to result in good user experience.
Now we are back with a totally new shortening engine! However, we now require all users to register an account. Registration will allow users to manage their own shortened URLs, see the number of hits and hopefully help us reduce the number of spam bots.