These are the so-called "egg-bombs".
In really early developing times, there even was a big discussion whether these bombs should really make a sound at all or not.
The sound was descibed as "oink", and one group was against it, thus they developed the "NO OINK!" signs. It looked like non-parking traffic sign with the egg-bomb in the background, and a red "NO OINK!" in the foreground.
Seemingly Lar or someone else succeeded: The sound was in eventually ...
