Reminds me of this (artist undertook "Guerrilla Public Service", donning CalTrans worker garb and modifying a highway sign to be more helpful to motorists): http://www.laweekly.com/2009-12-31/la-life/richard-ankrom-s-...

"The sign was so authentic that Caltrans officials let it remain in place for eight years, four months and 15 days, until its removal last month under a standard scheduled replacement. "