This is true. People abroad can also just put in any random address from Google maps anyway, postcodes supplied and all. And you can put a random name.
The unfortunate thing about this petition though is that it requires a fairly good knowledge of Hillsborough that most outside Liverpool do not possess (even with the excellent Panorama documentary). As its an 'attack' on an individual person, people with little knowledge of the event are (rightly in a sense) too ill-informed to sign it. I mean, I actually had to explain the details to my best friend before he signed it. This is all in contrast to the more obvious anti-institution Hillsborough petitions from before.
Have there been any celebrity-twitter based endorsements this time round? Rodgers, etc. It would be excellent if someone could get Daniel Craig to share it.