The city's renowned Mural Arts Program is engaging in a cover-up - for a good cause.

Mural officials recently draped a banner over the iconic Common Threads mural by Meg Saligman at Broad and Spring Garden Streets, for the first time using artwork as a temporary fund-raising billboard. Let's keep the emphasis on "temporary."

The banner across the mural showing Philadelphia high schoolers in classical attire makes a pitch for donations to "preserve this mural."

Saligman is renovating the mural, but funding for the project has fallen short by $20,000. So, Mural Arts director Jane Golden says the program is trying the banner. Initial plans were to keep the banner up through winter in the hope that it would raise enough money for the renovation.

With the mural partially obscured, the message is in-your-face clear: Without financial support - much of it from the private sector - the city's mural program wouldn't be the robust success that it's become in the last 25 years. More pointedly, the banner drives home the idea that, without repairs, the city's 2,600 outdoor murals could fade away.

Point taken. But the sooner this banner is removed, the better. It could violate outdoor-advertising rules. So it's good that Golden said Tuesday that the banner will come down after the holidays.

Of course, Mural Arts supporters can assure that no more banners are needed to raise funds - by showing their generosity.