Online Greeting Cards..??? Help Please?

Okay, well ive once singed this online card, it wasn't an e-card, or a printable one... You signed It then the moderator sent the link of the card, to the person it was for. I really need to use this site, or one very similar. Does anyone know i site i could use...? That my followers on twitter could sign;) Any help, is very appreciated:) Thank you.. x