QR codes (quick response) are similar to the barcodes you see in stores when you purchase an item, the big difference is that these are designed to be used with smart phones and can be used to direct users to a website, a geolocation (place on map), contact information, or even trigger an sms (text message). Unitags Costomized QR Code Generator allows users to generate a full color QR code with an embedded logo. Check out the example below.
Use a barcode reader program on your smart phone to scan the QR code and see what happens. Barcode Scanner for Android or Pic2Shop for iPhone (both are free) are two great starting points. You can include these codes on flyers posted in the buildings to have students or parents go to a web resource or have an event added to their calendars or even have students incorporate QR codes into projects to take an audience to an explanation or reflection on a piece of art, project or other display.