Why alter billboards so cleanly?

Put up November 19, 1981, at the corner of Cedar and Center Streets in Santa Cruz. Covered over January 8, 1982, after being up for 50 days.

The caricatures of President Ronald Reagan and Secretary of State Al Haig were borrowed from a Pat Oliphant political cartoon.

How Was It Done?

Why alter billboards so cleanly?

TIA wanted to employ the same techniques advertisers use, but to turn the message against itself.
A cleanly altered billboard throws a contradiction at people: it looks like a real billboard, but it can’t really be saying that, can it?
Surprise is a powerful method of getting attention, and ordinary graffiti is not surprising.
When done cleanly, the billboards stayed up longer.

“The change even escaped the attention of Vern Fitner, of the advertising firm of Foster and Kleiser which owns the billboard. Fitner recently drove by the billboard, but failed to notice the doctored message.”

Santa Cruz Sentinel March 4, 1981.

Additional publicity.