SAN FRANCISCO — It used to be that the only time you'd notice a bar code was at a store, maybe when a cashier scanned your groceries. But lately bar codes are showing up in more places around town — and getting more sophisticated.

You might have seen one cousin of the traditional bar code: Known as a QR code, this jumble of little squares randomly arranged within a larger square is popping up on everything from bus stop billboards to restaurant windows. If you spot one and snap it with your cell phone camera, the device can show you a website, photo or video related to the advertiser.

For example, Google Inc. is giving businesses stickers with QR codes that passers-by can scan. That brings up a link to a mobile version of a Google page where the business can post coupons and information about themselves. Soon the codes could lead to other avenues for connecting with customers in ways businesses can measure and control. That could help them target advertisements to the people who are most likely to respond to their entreaties.

Earlier attempts to get consumers to scan bar codes that link with the Web didn't get much traction. The 1990s brought the CueCat, which let publishers append their printed material with bar codes that people could scan with a handheld reader if they wanted to be taken directly to related information on their computers. The QR code (short for "quick response") also was released back in the '90s by Japanese scanning equipment maker Denso Wave Inc.

What has changed now, though, is that consumers are increasingly engaging with their mobile devices for more than making phone calls, texts and checking e-mails. And smart phones can easily download scanning applications that make it possible for product codes to leap from store shelves to the wider world.

The bar code on your box of cookies encodes a string of numbers horizontally that a bar code reader matches with information from a central database. That's how the supermarket scanner identifies the product you're buying.

These other codes, such as QR codes, can represent data horizontally and vertically. That means they can include much more information in a smaller space, and some of them can tell the scanning app on your phone all it needs to know about which website or video to pull up, without needing to consult a database. It's unclear how many of these codes are out there, but potentially billions could be created.

Google has been using QR codes since late last year to help promote hundreds of thousands of businesses in its local listings service, known as Google Places. The company has sent the businesses decals for their windows that say, "We're a Favorite place on Google" and include a QR code at the bottom.

The idea stemmed from Google's desire to have more of a physical presence with businesses and consumers, says Ryan Hayward, a product marketing manager for Google Maps who is heading the rollout of QR code stickers. For now, the codes lead to the mobile version of a business' page on Google Places. Eventually, Google might use the technology to pull up videos and lead to application downloads.

QRs aren't the only two-dimensional codes that could catch on: Since March, movie ticket site Fandango has allowed some filmgoers to get tickets on their phones in the form of similar-looking "Datamatrix" codes. The on-screen code is then scanned at the theater. Users don't need to have smart phones for this to work.