Here's Posner's explanation of his "ninja show" philosophy on his blog last month:
Basically a Ninja Show is where I tweet that I’ll be playing some songs [on] my guitar in the park at a certain time, and hopefully people come at listen. I got this idea from Amanda Palmer. Our first ninja show was in Ann Arbor.
What makes these gigs special is that they are not gigs. There is no stage, no microphones, no BS….just guitars and voices. This time, my buddies Chord Overstreet (whose song Hold On is one of my favorites this year, I may be helping produce it), Ryan Follese, Jamie Follese, and Adam Friedman joined me in what became a ridiculous jam session ending with our rendition of “Get Lucky.”
And here's the heraldic tweet:
Ninja show tonight in Cleveland. Edgewater Park, 7pm, free, acoustic, all ages. Detroit tomorrow, then Chicago either Wed or Thurs!— Mike Posner (@myNEWepISoutNOW) July 6, 2015