Overlaying Graphics on a Live TV Signal

Hello, I am a new member of this forum. In my office, we have an LCD TV in the lobby tuned to CNBC. I would like to find a way to overlay some graphics, specifically our company logo, onto the screen. My first thought was some kind of video capture card on a PC that is able to overlay graphics. Does anyone know of the right solution for this problem? I've googled all over the place but couldn't find what I was looking for. I know how to do this in Adobe Premeire with pre-recorded video, but want a solution for Live TV. Thanks in advance for your help.