street spam
n. Advertisements posted on telephone poles, traffic lights, and other public areas.
And while most every city, county and country in the world has street spam, the issue is coming to a head in Syracuse. "Some intersections you pull up to and you can barely tell the traffic control signs from the lose-weight and work-from-home signs," Worthen said.
—Brady Snyder, “Utah town may curb ad signs,” The Deseret News, April 08, 2002
2001 (earliest)
Citizens Against Ugly Street Spam — — is a non-profit organization dedicated to "the fight against the proliferation of unsightly, illegal advertising signs . . . for the sole purpose of stealing free advertising at the expense of the aesthetics of the community."
—Kim Canon, “Deleting signs an addiction for bandit,” The Houston Chronicle, March 21, 2001
Street spam is also called vertical litter and putting up such signs is called flyposting. Street spam is an example of a more general scourge called bandit signs.