In San Francisco, a street name stamped on a sidewalk corner serves a simple purpose: telling people where they are.

But an improperly stamped name has a shot at Internet stardom.

Each time a sidewalk in the city is paved or repaved, third-party contractors hired by the Department of Public Works ready themselves to stamp the intersecting street names into the wet concrete. They arrange fist-sized metal letter stamps in a row, backward in both order and orientation, then flip the whole thing over and engrave the name for decades to come.

Occasionally, though, something goes awry.

The resulting misspellings and backward letters may be cringe-inducing to some. But a guerrilla army of sidewalk typo buffs combs San Francisco's streets, with cameras at the ready to capture the freshest or funniest misprint preserved in artificial stone.

The enthusiasts share their prizes by uploading them to communal Flickr groups, then continue the hunt.

Thomas Rogers, 40, remembers the first beauty that caught his eye. At the corner of Missouri and Mariposa streets, a Frankenstein of a street stamp stared back at him.

"M1SSOR1," it declared. The "M" was an upside-down "W."

Rogers kept the typo in the back of his mind. Then, about six years ago, he began trying to walk more, hoping eventually to pass over every street in the city. Suddenly, "M1SSOR1" had company.

Through his city walks, Rogers has collected around 150 typos. Eric Fischer, an urban historian and cartographer, has logged more than 200 in his own set.

Still, many people, whizzing past by bike, car or bus, never notice them.

Way off Broadway

In Rogers' estimation, the concrete bungles happen at just the right frequency. Anyone who walks in the city will see one soon enough, provided they look down.

"If they were so common, that would be really irritating, because the competency of the workers or the ability to navigate would be compromised," Rogers said. "But they're infrequent enough that when you stumble upon one, it's like finding an Easter egg."

Not everyone is as charmed as Rogers and his ilk.

Frances Hochschild, 51, was "flabbergasted" to see that construction crews revamping sidewalks near her home at Broadway and Divisadero Street this month managed to stamp "BRODWAY" and "BROADWEY" at the same intersection.

"You see one mistake and you think it's sort of a joke, but then you say, 'Oh my God, not only did they make another mistake, they made a different one,' " she said. "It's not hard to spell, and the street sign is right on the corner. It's beyond belief."

Public Works fixed the fraternal-twin typos on Broadway after The Chronicle asked about them. It was easier to get the repairs done, department spokeswoman Mindy Linetzky said, because the contracted job was ongoing.

Older sidewalk typos, however, aren't likely to be fixed unless the whole curb is redone, which usually happens when streets are widened or curb ramps are modernized. Public Works says it doesn't have the resources to fix old typos - a $300 procedure.

That suits the typo hunters just fine.

Street name stamps are rare outside San Francisco. In many places, the only sidewalk stamps are construction stamps, the result of local governments requiring contractors to stamp their name and the year (often one in the 1930s) on new sidewalks as a form of quality assurance.

Impressive custom

San Francisco is among the few cities to systematically engrave street names on every corner. Some theories suggest the practice began in 1906 because people had a hard time recognizing their surroundings after the earthquake that April.

Fischer, though, found the original ordinance, which went into effect Nov. 6, 1905: "In all artificial stone sidewalks hereafter ... shall be impressed in letters or figures ... the streets so intersecting."

Records that might elucidate the city's motive were most likely lost in the 1906 fire. But as Fischer notes, street signage was mostly voluntary in that era, limited to buildings that chose to include the street name in the facade.

Citywide street signs, posted on building corners and on poles, didn't debut until the early 1920s. Before then, sidewalk stamps were all people had.

Now, of course, signs dot every corner, and residents have Google Maps in their pockets. The stamps, freed from their chief duty, are free to be a little bit off.

Some errors shed light on how the stamps are made. Arranging a word's mirror image is apparently no small feat - many an "S" is reversed and streets tend to be abbreviated as "TS." A fan favorite, at Howard and Second streets, reads "TS DRAWOH," with the "D" backward.

Signs of resourcefulness

Other stamps tell the story of a concrete crew's resourcefulness in the face of a missing letter. An upside-down "A" becomes a makeshift "V", and a "1" stands in for an "I." With some embellishment, a "P" transforms into an "R." Some letters are hand-drawn.

Still others appear to betray workers' impatience ("SACTO").

At its best, a typo can give the street name an unintentional, even poetic, new meaning.

They can become a command ("LEAVEWORTH") or a war cry ("YERBABUNE"). Some turn the familiar ("Geary") into the mundane ("GARY").

Some take flight with a neighbor's touch, like the "BRAYNT" in the Mission that was spotted and underlined with a squiggly red spell-check line.

When a street name is truncated by a partial paving job - one sidewalk square replaced and an adjacent one left untouched - less can mean more, as in Frederick becoming "ICK ST."

To Fischer, the weird and flawed things about San Francisco make it special. The typos are compelling, he said, precisely because each mistake reveals the human hands behind it.

"Errors are really interesting - they're an indication of process," he said. "Perfection doesn't tell you how it was made. It's when you see the scratch in a piece of wood that you understand how it was done."

A sidewalk, he said, is "not just some hunk of concrete. This is something that somebody made. It humanizes the city."

What's not working

Issue: Contractors sometimes make spelling errors when stamping street names into sidewalk corners - though some residents consider the typos a unique San Francisco treasure.

What's been done: If mistakes are spotted while work on a corner is ongoing, crews will fix it. But fixing long-standing typos is not a priority.

Who's responsible: Fuad Sweiss, Department of Public Works deputy director of infrastructure and city engineer, (415) 554-6940

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