Matt. As I ride my bike through the streets of San Diego, I see various symbols, usually with arrows or dotted lines, painted on the pavement. These letters include things like “MH, ” pointing to a man hole; “GV” which must mean gate valve and other less esoteric lettering such as "TELCO," which even to my mind must mean telephone company. But I also see the symbol "USA” splotched on the ground, which for the life of me I can't figure out. —The Bike Rider, @prodigy.cotr

Figure this: The Ubiquitous Sidewalk Art in Urgent Signage Areas is the work of Underground Services Alert. That’s Underground Services Alert of Southern California, a nonprofit consortium of gas, phone, electricity, water, arid sewer groups, some builders — anybody, except maybe gophers, with an interest in all the junk snaking along under our feet. If you’re planning to excavate, by law you have to find out what kind of cables or conduits you might encounter. Call USA and they’ll alert any utilities that could be in jeopardy, and they'll send out guys with maps and spray paint to mark the locations of things they’d rather you wouldn't hit. (Those are the arrows and dotted lines and circles and initials.) The “USA" just means it was done through the auspices of Underground Services Alert, and it’s official. In other words, it’s the official map of exactly what your backhoe should aim at to break that big water main and get your construction project on the evening news. „