Traffic calming measures, unless implemented entirely incorrectly, are not unmarked. To have them unmarked would defeat the purpose, which is to indicate that the driver of the vehicle attempting to navigate the street must slow down. It is not in the interest of those living on a street with traffic calming measures to have drivers cross the traffic calming measure at a high speed.

Narrow or winding roads, or roads with no central marker are calming techniques often unaccompanied by signage

Okay, but many of those traffic calming measures are a big concrete block in the middle of the road.