Bonnie Radcliffe

I don't know how it happened but several months ago some marks started coming out in the corners of my Word files. I include a pic for you to see it. I have been looking for in the Word help for some time now, but I haven't even found out what that marks are!! I have tried to attach another snapshot, but it just doesn't get attached. T_T Do you know what that marks are?? And, what's more, do you know how to get rid of them??