Michael Bay is filming Transformers 4 in Detroit where it's reported that lots of explosions are a part of the shoot.
No surprise there really, but what is interesting is the following set image of Mark Wahlberg featuring some kind of Transformers sword.
TransformersLive speculates it might be a Cybertronian key.
It's also possible that Wahlberg's character could have invented it as he recently stated he is playing an inventor trying to make ends meet, while evading questions on the Dinobots.
You can also check out video footage of the Transformers 4 Detroit shoot below as well.
Transformers 4 has a Summer 2014 release directed by Michael Bay and starring Mark Wahlberg, Jack Reynor, Nicola Peltz, Sophia Myles, Li Bingbing, T.J. Miller and Kelsey Grammar.