I designed and made this bat-signal a while ago for a friend. Using a 12V white LED strip it actually works and projects a bat-signal onto the wall or roof (Save Gotham like a bystander - phone a friend). You will need to block off 2 of the 3 LED's on the bank otherwise the multi-light sources will eat the shadow. If you come up with a way to make it even brighter, please do share as I'm open to different (albeit safe) lighting sources.
I take a lot of time designing and sharing my designs, so please donate the 2min it will take you to upload a photo of your makes (seriously, it's the least you can do) :)
Just cut a clear piece of plastic (overhead transparency will work fine), and glue the Bat symbol in the middle. Glue the support into the base with superglue. The rest is 3D print and press fit together. Add some lighting and you'll be saving Gotham in no time.