Since they were introduced last December, onboard advertisements have quietly inundated vessels Washington State Ferry system-wide, and become an increasingly valuable revenue stream for the cash-strapped agency.

The program began with just one advertiser, JanSport, which spent $39,000 for wall, door and car-deck murals on the Wenatchee and Tacoma.

Over the last 10 months, roughly 20 more advertisers have purchased advertisements on ferries, which have been featured on every route in the system except for the Port Townsend-Keystone run. Advertisers pay anywhere from $1,200 to $180,000 for the marketing campaigns, which typically last four weeks, according to Skip Vose, chief executive officer for Trans4media, which markets the ads for WSF.

“What we’re trying to do is bring as much revenue to WSF as we can, and do it in a way that is pleasing to the riders,” Vose said.

Pleasing riders, Vose said, means making sure ads are tasteful and don’t “clutter” the boats. Displays have been limited to sleek surface-hugging decals spread on walls, stairwells, doors and floors. Ads usually feature large images, subdued colors and simple text.

Vose said his company encourages advertisers to bring value for riders. Jansport, for example, held onboard drawings for free backpacks. More recently, organic foods company Seeds of Change supplemented an elaborate series of ferry murals with free samples of its products.

Riders can expect a wider array of ad styles in the future.

Vose said his company has been working with three-dimensional displays. It has mocked up a life-sized cutout of a car that could be placed on the car deck to promote an automotive dealership.

Trans4media is considering offering new onboard services that would be paid for by a corporate sponsor. An onboard concierge, for example, could help riders make dinner reservations and book hotel rooms.

Ads have been purchased by companies with national and international markets, including JanSport and Lufthansa airlines, as well as Northwest-based companies and government agencies, including the Department of Ecology.

Puget Sound Energy is running an ad campaign on five boats this month, to raise awareness for its Green Power Program, which allows customers to contribute money for the energy company to add alternative energy to its system.

Vose said Trans4media is hoping to attract smaller, local businesses with ad packages in the $500 range.

Rebekah Anderson of PSE said the ferries seemed a logical way to reach customers.

“We felt that commuters who use public transportation would be interested in conservation and renewable energy, and it gives us great range,” she said.

Bainbridge writer Susan Wiggs has been thrilled by ferry ads her publishing company purchased to promote her novel, “Just Breathe.” Wiggs held a book signing onboard the Wenatchee as well.

She said she has received many positive comments about the poster-sized ads, but fielded a call from a ferry rider who was irate that she was “plastering” ads for her book across the boat.

Wiggs has her own view of ferry advertising.

“I think anything WSF can do to make money without raising fares is great,” she said.

In fact, advertising is one of a limited number of tools WSF has used to raise money outside of the farebox and taxpayer support.

Even before the glossy JanSport ads were rolled out, Certified Folder Display service maintained brochure racks on the boats and concessions contracts have provided steady money.

WSF also charges an hourly rate each time a television show or advertiser films on a boat. It’s a popular service and the iconic, green-and-white vessels attract big names.

In the last four months, ferries have hosted dozens of film crews, including “Rachel Ray Show,” “Extreme Makeover Home Edition” and “Shrek the Musical.” Hourly rates begin at $300, and increase depending on crew size if ferry resources are required, according to WSF Operations Administrative Manager Jim Fletcher.

But those user fees accounted for just $25,000 in revenue in 2007, a meager sum when compared to just one month-long ferry advertising campaign.