I can't imagine producing a poster for ANR that doesn't have a QR code somewhere on it. 
A QR code is a two-dimensional code, which can be read by mobile phone cameras using a free software QR reader application. These variations on bar codes were developed in Japan to inventory trucks and have been used on UPS packages and airline boarding passes for years. These "quick response" codes are popping up everywhere but not everyone knows what they are...yet.

The latest generations of smartphone models (iPhone and Android OS) have easily accessible scanner apps and smartphone owners are more likely to make use of QR codes. Do you question how big an audience that is? Sales of smartphones in 2011 is expected to equal the number of not-so-smart mobile phones (feature phones) in the US. There are over 292 million mobile phones in the US today. According to Nielsonwire.com, as of December 2010, nearly a third (31%) of all mobile consumers in the United States owned smartphones. Only slightly more males than females will buy them this year and "Hispanic Americans and Asians are slightly more likely to have a smartphone than what their share of population would indicate." So, if your Cooperative Extension clientele are male or female, or white, Hispanic or Asian, you probably have an audience for QR codes.

What does a QR code do?
QR codes are used primarily to drive traffic to your website, Facebook and Twitter accounts. They are used heavily in marketing and social media campaigns.

There are several applications but in general, they provide a way for smartphone users to collect information from your print material quickly. Instead of writing down the URL found on your posters, signs, newsletters, etc., your audience scans the code with their phone and they are instantly linked to your site, online publication, a video, calendar event, or anything else you can place on the web. You can also simply put messages in them, up to 1400 alphanumeric characters. 

QR codes can be placed on signs, kiosks and printed material to help cut down on excessive use of paper and subsequent littering. You don't have to hand anything out to smartphone users since in only a few seconds they will walk away with your link in hand.

How are they made?
By using one of the many online QR code generators you can drop in a URL, calendar event or text message and the graphic code is immediately generated. Copy or download it, then apply it to your document. Because they contain only blocks and no curves, they can be enlarged infinitely which is why it is easy to produce signs, even billboards with it. 
I'm partial to this one: http://zxing.appspot.com/generator/. It formats the different types of information nicely like events, contact info, and URLs rather than those that are just oriented to URL coding.

Examples of QR Codes
QR codes are found on tattoos, stickers, car magnets, yard signs, business cards, mouse pads, t-shirts, name tags and anything else that is printed.

This video shows your more about marketing with QR codes.

How can they be applied to Cooperative Extension?
Take a look at how the University of Arkansas placed QR codes in their Division of Agriculture Strategic Plan; see page 5, codes link to videos.

Here are some other ideas-- (scan this one and take the list with you)

• link handouts and books to online resources
• link locations with information about resources (both physical and human)
• orient visitors to a location
• complement fieldwork with online information
• link nutritional objects to calorie counters (and other health applications)
• connect scientific equipment to how-to videos and instructions
• link a presentation slide to online information (e.g., to complement conference presentations with online information)
• provide text information
• pose questions or quizzes
• pose scenarios (e.g., how would you use this item in this situation?)
• polls and surveys
• discussion forums
• audio (including multiple language formats)
• link to instructors/mentors available for live-chatting
• add them to recipes to show processes.
• 4-H exhibitors could use them to link back to Web sites and videos showing how they progressed over time.
• include in 4-H learning guides to demonstrate processes.
• welcome signs to link back to more informative Web sites.
• on signs in fields where research is taking place so a learner can get more information.
• conference name tags can have QR codes to provide more information about a participant.
• promote events
• create virtual tours of areas of interest, each QR code gives directions to the next location.
• add them to plant identification tags.
• link to a Google map you created.