I tried pins and buttons, from the past three years I have accumulated nearly 300 buttons. However, they don't work particularly well as a kind of random thing. When I wear a Robodox shirt, I find that someone usually strikes up a conversation with me and I get to expose someone new to robotics in some way. In the same way, I get the same responses wearing a vex volunteer shirt. Plus, it's a bit easier for me to throw on another teams shirt to wear for the day than to cycle my buttons. And some teams have really nice looking shirts
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2011: Head Scout
2012: (figure)Head Programmer
2013: Head Programmer, Chief Strategist, Outreach Executive, and Driver