Step 1: Get your stuff together...
An LED electronic candle (flickering tealights)
A plastic hand - IKEA Patrull safety bumper caps
Pin backing clasps - found in the jewelry findings/notions at the craft store
Hot glue gun to put it all together
Hacking tools like a utility knife, screwdriver, wire cutters
CAUTION: Know how to use your hot glue gun and handle hot glue only when cooled or you will burn yourself.
Step 2: Hack electronic candle
The battery, switch, and LED are all in one unit. Bonus is that it flickers so it animates the light a bit. Only drawback that it is a bit dim so it doesn't really light up the thick translucent plastic hand. I guess you can switch out the LED for a brighter one.
Crack open the electronic candle by prying open the cover. Insert a utility knife in the seam to crack open any glue. This one is held together by a post and mating post on each side of the case. It is snap-together construction so it is easy to pull apart.
I also pulled off the silicone "flame" diffuser. You can use it if desired but I only wanted the small bare LED.
Step 3: Apply part A to part B and mix...
See how it fits on the back of the plastic hand.
The mounting post was too high to make it fit nice so I clipped it off with wire cutters to size.
I suppose you could also peel away the hand from the clear support plate on the bumper to form various gestures. You can make the "Rock On" sign or the "Thanks for cutting in and getting my parking spot wheredya learn how to drive" sign.
Step 4: A little dab will do ya...
See where the mounting posts lay on the back of the plastic hand.
Apply a blob of hot glue at those points and press together.
Hot glue the pin clasp on the back of the LED unit.
I would place the pin clasp a little higher on the LED unit so that the finished button doesn't droop from the weight when pinned to clothing.