What system or device is this from? It doesn't look lke this matches up with the CC/5x0, or, well, any machine I can remember seeing.
Ports of approximately that shape and size did get used for a couple different things- ADB and serial (printer/modem) for starters, as well as S-Video in some scenarios (although not many s-video ports were directly on the motherboard, 840 was, IDK about the 660.)
When this cover is installed, what port is it? Is it possible it's a labeling oddity and that icon is for the Kensington lock slot above?