For whatever reason, I just can't seem to google the answer to this question. It seems like it should be pretty straightforward, but my Google-fu is weak.
Recently, I noticed one of my user develop presets changed its name to have a plus appended to it. So, orginally, my preset was something like "My Develop Preset," but now it's "My Develop Preset +". I've tried changing the name, and it appends the plus sign to whatever name I choose.
So, what does the plus mean?
It indicates that particular preset is selected to be applied during a import.
In your preset list right click on the name then deselect "Apply on Import" and the plus sign will go away
(and in the Import window Develop Setting will change to None)