Done Portal signs are not working

Whenever I try to place the sign with the text 'portal', it just says 'Not quite.' and the portal sign is not created. What am I doing wrong?

 

Are you creating your portal like this?



Also, try to place the obsidian before the sign.

 

1.64 does not use the sign, light it as you normally would.

 

Well it says it does on the wiki: