Witcher 3: activating alternate signs
Solution 1:
The 'Points in Branch: 0' at the top of the Signs section is just telling you that you have not currently spent any Skill Points on signs. This is useful information because the rows in the table are unlocked as you spend more points in the table.
So to begin just select an entry in the first row and use 'Acquire Ability'. Then you can continue to upgrade or acquire abilities.