New Table Cameras Question

I went to a friend's wedding over the weekend and she had table cameras. It happened to be placed right near my seat, so I noticed it right away. But towards the end of the night, two of the people on the opposite side of the table said, 'Oh, I didn't know there were cameras.'

That worried me that the same thing would happen at my wedding. Besides the little sign that comes with the camera giving instructions (which she did have), is there any way to make it obvious or to let it be known that the cameras are on the tables?