I just made it. It's 23:09 Pacific.
So I can indicate only support for an registered petition. Can I vote against it?
I really don't like that one to increase stacking reward per block.
A petition/CLAMour must prove itself on it's own merits.
It must prove support by users pro-actively supporting it.
If you do not wish to support it, you must do nothing.
The blocks you stake will be interpreted to 'not' support by virtue of how the system works.
Essentially, not specifically supporting it is a default vote for "No Change".