How can i sign?

The cup is not planned or announced. When it is you will see a news post about it and be able to sign up via the "Events" tab in the upper navigation panel.

League of Legends Cup #5
Date(s): July 16 ~ 20
Website: http://ungl.org
Gametype: Summoner's Rift
Max Number of Teams: 64

From League forums Red said it

Link me this post?

http://euw.leagueoflegends.com/board/showthread.php?t=755271

I see you replied in the thread i hope i helped in some way! :D

Yeah I've emailed some people I know at Riot also to find out whats going on here. Bare with me :(

Im kinda sad tho, but cant wait till i can join some tour for league of legends :D