A website that I visit was warning about ACTA and had a link to this petition:
http://www.avaaz.org/en/eu_save_the_internet/?tta
The EU Parliament will make a decision on ratifying it in June.
To sign the petition you are subscribing to the site and receive an email with these links:
It would make more sense to me to have these links on the petition site as well so people would know why they should sign it but I guess the ones who made the website considered that people who arrived there are already informed.