Actually, turns out it's his wife's bike...
http://greenwoodphinney.komonews.com/news/crime/mcginn-who-borrowed-my-wifes-bike/623547
"Seattle Mayor Mike McGinn sent out the following tweet on Wednesday night: "I know I've been encouraging people to ride bikes more, but I didn't mean u could 'borrow' my wife's bike w/o asking.""
http://greenwoodphinney.komonews.com/news/crime/mcginn-who-borrowed-my-wifes-bike/623547
"Seattle Mayor Mike McGinn sent out the following tweet on Wednesday night: "I know I've been encouraging people to ride bikes more, but I didn't mean u could 'borrow' my wife's bike w/o asking.""