I'm not planning to shoplift, I'm just curious.
you can use broken glass, and make it safeWhen you put it on the poster glue it on then when its where you want it take a paint brush and brush glue around the edges and a small coat over the topThat would keep the glass on pretty wellYou could also take a c.dand smash it up pretty good and the reflection on it would make it shimmer like glassAnother bonus with the cd is you can put clear packing tape on the back before you break it and that way it'll stay all together and you can take scissors and cut the shape you want around the broke pieces.
go get sea glass at a walmart or dollar store its smooth and not sharp but is same as glass just polished
use Plexiglass hard plastic
With work you can get Plexiglas to look like pieces of broken glass, but it will not break like glass (although I have not tried it when if is frozen.) If you break a piece of glass, then take the black sandpaper called emery cloth and wrap it around a dowel or round pen, you can stroke the corners and take off the sharpness with very slight reduction in the crispness of the edgesYou can also do this with a small knife sharpening stoneThen you can glue it in place (or apply spray adhesive to the mount and stick the well cleaned glass on You still have the problem that the glass on the project can still be broken by hitting itThe stiffer the mount, the harder it will be to get pieces off.
A bag made out of aluminum foil will work.
