In the effort to establish standards that will encourage the acceptance of electric vehicles, there has been much wrangling over the development of a universal design for the plugs that connect battery chargers to cars.

That is not the only EV debate under way, however. A less contentious, but still important, issue -- the look of the road signs that tell drivers where they can top off a waning battery -- has yet to be resolved.

Of equal urgency, there is no broad agreement to define the signs that warn drivers of vehicles powered by internal combustion engines not to park in designated charging spaces -- a nuisance that EV owners call "being "ICEd."

An estimated 5,000 public charging spots are available nationwide, according to Plug In America, an electric vehicle advocacy group, occupying parking spaces on city streets and at shopping center parking lots. Settling on a standard set of signs with an instantly recognizable logo, like the symbol used for handicap parking spaces, will be key to expanding the public charging network, said Richard Lowenthal, chief technical officer at Coulomb, a Campbell-based company that makes charging systems.

He knows this from personal experience. In search of watts for a Chevrolet Volt on a recent trip to the airport near San Francisco, he used a smartphone app to locate a charger on the first floor of a parking structure -- where he discovered that the first floor was "a big place." Running late for his flight and searching for the charger provided a lesson in the need for better directional signs, he said.

Standards for traffic signs are in the Federal Highway Administration's Manual on Uniform Traffic Control Devices. The manual's 2009 edition includes a sign with the image of an EV charger that can be used, along with arrows, to guide drivers to the charging spot; the latest version of the symbol resembles a gas pump with an electric cord and plug attached. But the manual does not specify a sign to clearly indicate that a spot is reserved for charging.

Most state and local transportation authorities conform to the federal standards to mark public roads. But for chargers off the public road, EV station owners place directional signs at their discretion, Lowenthal said.