Among the winners: the National Association of Realtors, Chicago Ventures and OCA Ventures. : Last week's IPO of San Francisco-based DocuSign created a big splash that rippled all the way back to Chicago.One of the big winners in the $629 million deal was Second Century Ventures, a strategic venture fund run by the Chicago-based National Association of Realtors, which was the fourth-largest shareholder. It sold 1.6 million shares for $46.4 million at the $29 IPO price on April 26. Its remaining stake of about 4 million shares is worth about $165 million.How did association get in so early?