On Election Day, many people who perform their civic duty proudly wear a sticker that says "I voted" – the photo says the same thing.

在选举日这天，很多行使公民责任的人会自豪地佩戴一枚“我投票了”的贴条。 自拍照片想要表达的含义是一样的。

youdao

This photo shows a warning which one of our crew cars received (the driver actually had a 'sticker' allowing him in the lane - but that's another story).

BBC: Is TfL Games Lane 'warnings not fines' tactic working?