SmartMLS has electronic document signing available through the Authntisign section of Instanet/TransactionDesk.
After you sign into www.smartmls.com, click on Authentisign in the MLS Products & Resources section:
Once you are on the Instanet main menu, you can open up Authentisign by clicking on the 3rd icon down (it looks like a pen) on the left side of the screen:
Here is an article that goes through the entire process, step by step.
Here is a video that goes through the process of starting a signing with Authentisign.
There is an entire library of videos and other support documentation for Authentisign located in the Instanet Help section (click on the question mark icon at the bottom of the list):