"It's not like the law is involved, unless you're tagging a McDonald's ad," Perez-Boza said, laughing.

"I had someone tag one of my work-in-progress murals.

"The silly part about this was how they displayed it.

"My wall was about 15 feet high, 20 feet wide. Their mark was no bigger then six inches."

You can see some of San Francisco's best murals and other art at websites for the Clarion Alley Mural Project; Carlos Daniel Perez-Boza; Mats Stromberg; SF Mural Arts.