Little plus sign in the bottom right of cell

I am new to Numbers. I just set up a spreadsheet with a date. I went to the inspector to specify the format for the date, I did the time as well. When I went back to my cell there was a plus sign which I took to mean that there was more content. So, I looked and saw the time. I took out the time in the inspector but the plus sign is still there. Does anyone know why?