For a moment I wondered how he knew. I do not carry a bicycle helmet around. Neither do I have a U-Lock sticking out of my back pocket. Nor do I wear t-shirts with pictures of bicycles or bicycle slogans on them. And then I remembered: I was "wearing" a wheelset. A full wheelset, with tires attached. I was bringing the wheels to Framingham - an hour long trip on subway and commuter rail - and rigged up a system inspired by carrying my skates around.
Something similar happened yesterday, when I wrangled a floor pump into my handbag and walked to my art studio with 1/3 of the large, orange pump sticking out. When I stopped for a coffee on the way, the person behind me in line startled me by saying "That's quite a pump you got there!" Once I realised what he meant, I considered explaining that my hand-held pump does not fit Shrader valves. But thankfully it was my turn to order coffee just then and the person was spared that narrative.
What is the most unusual thing you've carried off the bike that distinguished you as a cyclist?