Someone correct me if I'm wrong, but I think the absolute first sig campaign was earlier than 2013. I remember browsing very old posts, and I stumbled across the thread where the idea to rent out signature space for advertising was floated, and I could swear it was 2011 or thereabouts. Either way, nine years' worth of data are more than enough to satisfy my curiosity.
The first one is in 2011 but I don't know we can considered it as a signature campaign from a company or only a signature campaign from a member.
[CLOSED] up to 50 people, get paid 0.10 BTC to change your signatureThe first idea is 3 months before this one.