A small string of dots with no words generally represents a silent disapproval. One could say that these dots on their own could be seen as the feeling of what facepalming would be, without going through all the trouble of actually typing it out. However, dots being what they are, tend to convey the emotion rather than an actual statement, so that each reader may have their own understanding of how they think the author is feeling. An example of this is as follows:
Michcat could see James' "..." as "Why are you attempting to build a second Riddleport, and with no money at that," where as Anithola could see the "..."s as "Why are you wasting time not putting the theater in port silver," while my own perception would be something along the lines of, "Called it." Of course, James himself may have meant something else, like "This isn't getting off the ground," "Why is an Earthspawn trying to be friendly towards everyone, this breaks the lore," or something as vague as "Is this kid serious?"
Hopefully I've explained James' last post thoroughly enough for you.