But you can use any decal and it will shine the outline on the ceiling.
Step 1: Bat Signal Materials
1. Compact mirror from Walgreens $8
2. 4 x magnifying glass from widgetsupply.com $8
3. 1" batman decal from eBay $2
4. Nursery night light that does not shine light on ceiling. I built mine from wood and an old lamp - led bulb was used
Step 2: Installation
Mount mirror at 45 degree angle to light source ( light should shine up on ceiling but not yet focused) . Remove outer case from magnifying glass. (Note - not all magnifying glasses are what they claim).
Play with the mirror and the magnifying glass until you get a sharp focused bat signal - good luck all!