I have found that in the long run flat black spray paint is the best method for "stealthifying" a camera that has unwanted logos, lettering or shiny parts. Sharpies don't really work all that well and don't last too long. Black tape can peel or get sticky sitting in a hot vehicle on a sunny day.
The "best" method is to remove the front of the camera's case and do a proper paint job. This task is not for everyone but really it isn't all that hard to do. Like many dash cams the case simply snaps together and with some careful prying it will pop open. After that it should be easy to temporarily disconnect the microphone and LED from the front of the shell. Once you do this you can spray paint the shell and when you put it back together you will have a nice professional looking and durable paint job and a camera that is much harder to see from outside your car.
In this photo borrowed from the
DCT G1W comparison page you can see how the case comes apart and I've added some arrows pointing to (some of) the clips molded into the case that you'll need to press in to open it. Once you get the first one or two open the case should come apart fairly easily.
I painted the front case of my GT300W as shown below. The case of the GT300W fits together almost exactly like the G1W. Since I have no use for the LED they put on the front of these cameras I disconnected it permanently and painted over the LED lens, thereby improving its "stealthiness"".
Almost any flat black spray paint suitable for plastic and metal will do a decent job and in the above photo I used some cheap paint I bought at Walmart. It's fine and it has held up very well. In the meantime, I've found a much better product to recommend........Rust-Oleum Camouflage Paint. It is the flattest, most non-reflective paint you can buy and it is perfect for painting dash cams.