The XIXth Century Search Engine was released as promotional media for Assassin's Creed: Syndicate.
Riddle 2: type "Victorian Mirror". You'll get a mirrored text. Type "show me the road" and you'll get the second code: YND6.
Riddle 3: type "God save the Queen" and a page should show up. If you click on the last words it should disappear and the search box changes in: "if you promise to Protect the Londonians from oppression you’ll be rewarded for it". If you do a search with that, press Found A Hidden Gem and you'll get the last code: S3RK.
The reward for completing the three riddles is:
By searching Playstation, press Gamodrome. On the right is a code to unlock Edward and Elise Outfits, but it's PS4 only.