Batman is known for throwing his own brand of boomerang, also known as a 'batarang.' If you have one of these handy accessories on Halloween, pose like you're about to hurl it at the picture taker, but don't actually do it! They'd probably frown on that type of thing.
Batman is also well known for always hiding in the shadows. Every time Jim Gordon turns around? Gone, nowhere to be found. Batman loves to just disappear, and that's what this pose is doing. Block your face with your cape, and give a stern look.
Cross your arms, stand up straight...as Batman, that is. When you do this as old Bats here nobody would dare mess with you, not even the Joker or the Penguin! That's because this stance means business... bat business to be exact. Confidence oozes out of him and says without saying, "I protect Gotham, and thus, you."
Batman doesn't use guns, because he doesn't believe in killing. He only believes in justice. This pose, with your hands tucked behind the cape, looks like you're ready to strike your picture taker, but of course you aren't going to do that. He's a master of intimidation, so you should be too!
Perhaps Batman's most famous pose is him perching on a gargoyle of some sort about to pounce and glide down to the streets below where he will bring justice to those that need it. Do this pose and you'll always look cool, especially in the deluxe costume!