Whoever has control of the meeting(host/participant) would be able to add multiple signatures on a document.
Simply click the "add signature" button on an introduced document in the room then change the name indicated on the top left section of the document. Add your signature on the blank canvass then click the "paste" button to add it to the document.
In case you need to use a signature file on the computer, follow the same process by changing first the name that will appear on the signature then hit the "browse" button on the top right of the page. Look for your saved signature on your storage drive then click the OK button