One of the most readily observed bee communications. Look for one bee holding another bee with its front legs and shaking:
Notice how the held bee stands still while the signal is performed.
The behaviour is generally correlated with a need for more foragers, and possibly serves as an invitation for inactive or non-foraging bees to look for waggle dances and prepare for foraging. It is performed most often by foragers after their first few trips to a nectar source before they start waggle dances.
It has also been suggested that the shake signal might really represent a more general "it's time for a new activity" message, which is then interpreted according to context.
Bees have also been observed to perform the shaking signal on queens. Performing the signal than ceasing to do so just prior to a swarm, mating flight or on mature queen cells particularly after one queen has emerged and before an after swarm.
This behaviour has also been referred to as the vibration signal and once upon a time as the joy dance.