Those strange looking squares are called QR codes or Quick Response codes. You use them with the camera on your cell phone.
The code has stored in it contact information in it about who is doing the advertisement or whose sign it is usually with a web site and other information. It allows you to use our cell phone to quickly get information about the place.
The strange characters are squares that are made of lots of smaller squares and the pattern of these squares stores the information. They are considered two dimension codes as opposed to the bar codes we see on everything in stores that are one dimension. By one versus two dimensions we mean that in the one dimension the code is just across in single row. The two dimension code has stuff stored in it vertically and horizontally.
You can get an app to put on your cell phone that will read the codes using the camera on your cell phone. You can either buy the app or get a free one from the app store (place online thru your cell phone that distributes apps (small applications for cell phones and tablets)).
We will see more and more QR codes in our world. You see them in advertisements in magazines and newspapers now along with on some billboards and some real estate companies have started using them on their For Sale signs. You also see them in emails in place of signature lines so that the person has what may have been a list of contact info and credentials in the QR code instead of written out on each message or in a v-card (virtual business card) link at the bottom of the email.