What Are Android Pins?
Android pins are goodies given away by Google to promote their operating system. Most of them were distributed in the 2011 and 2012 editions of the Mobile World Congress. Here is more information about them (how you could collect them, where to get them now, ...).
Android Pin at Amazon
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(price as of Apr 3, 2014)
How Could You Get Them?
The idea was simple. Google gave these collectibles to some partner companies which in turn were giving them away at their stand to attract more people.
For some stands, these pins were just free to take, while in other situation, you needed to talk to some representatives or even complete some simple tasks (complete a poll, answer a questionaire, download an app, etc...).
The list of participating stands was available on the Android website, the official website of the MWC event and even in the MWC app (at least in 2012).
Here are some of the 2012 Android pins:
An interesting part of collecting these items was also the trading that was happening, some of these pins being more popular than others, or harder to get.
One of the best tip about collecting them at MWC was to start early, check the list of stands to visit etc... Some stands were out of them after the first 2-3 days.
Missing at the MWC 2013
The MWC 2013 was a turning point as some big actors were missing. Android/Google did not even had their own stand this year (vs a very big one last year with a slide, goodies and everything...).
MWC 2013 was also a big disappointment for pins collectors: none were distributed. No other Android goodies either.
So Where to Get Those Pins Now?
If you missed them at the congresses, don't panic, you can still get them on eBay. Those pins show up there every now and then and are generally for sale at a decent price.