The e-signature specialist will be joining a major stock market index. Shares of DocuSign (DOCU 7.89%) charged out of the gate on Tuesday, surging as much as 9.3%. As of 12:50 p.m. ET, the stock was still up 8%. The catalyst that sent digital signature and contract lifecycle management specialist higher was an announcement the company would be joining one of the premier stock market indexes. Meet the newest member of the S&P Midcap 400 An announcement that dropped after the market close on Monday revealed t ...