The petition is called the "Crytek, We Care" petition, and states:
In response to today's Crysis 2 Beta leak, we who sign this online documents pledge to purchase a legal copy of Crysis 2. We also hope that this document shows that Crytek has a loyal PC fanbase that wishes to support their work, not rob them of it like the pirates who have constantly damaged our reputation as a gaming platform. Crytek, we care.
The online petition can be found.