The attached odd symbol appears every now and then on a PowerPoint slide (the symbol is just the white part, the black is the background of the slide). It can only be seen on certain computers (the problem being that the computer that I create the slideshows on doesn't show them while the one that projects the slideshows to the big screens does show them). Has anyone seen this before and can give me some idea on how it would be appearing and how to prevent it?

Thanks in advance.

Attached Images

Symbol.png (1.4 KB, 12 views)