In the early 20th century, parking lights were required in some states to be used whenever parking in an active roadway. In 1928, Ford used the side or cowl type lights for this purpose in the states where they were required. Later in the 1928 production year, the TWOLITE headlamps with there distinctive lens replaced the old single bulb headlamps with the fluted lens. The TWOLITE completed the legal requirements for parking lamps in those states that required them. They were eventually required for all cars and still are to this day in the USA.
Cowl lamps had a distinctive look that was popular with some so they were offered to any perspective customer as an optional part of the purchase package. Later in 1930, they became a deluxe car standard equipment but were still optional on standard cars at extra expense. This kind of stuff would give dealers a little extra on the deal similar to painting wheels to mach the accent stripe on the model A cars.