There are Source IDs in my SmartLink reporting that I did not create. Where did they come from?

Source IDs populate in the dashboard whenever a "sid=" is found at the end of a SmartLink when clicked, and that information is sent to Chartable. Chartable does not create SmartLink Source IDs. 

Any strange Source IDs could have been created by the browser the user was utilizing, or the sites that the link was posted on. Unfortunately, Chartable does not receive any additional data to "see" where Source IDs are coming from.