Microsoft Tag is a fun wheeze of a technology….here’s mine, linking to this blog.
It’s interpreted by a mobile phone app and can do stuff like link to a mobile web site, dial a number, send your location for location-aware stuff etc – get the picture 
You may have seen this before but now you can convert the basic tag into a picture which tag interpreter can decode (it’s all about where the colour areas are). This all seems to be easy to do – check how to do it.
