If you deposit your number plates at the Road Traffic Office, your car insurance is suspended during this so-called suspension period until you use the plates again.
Some of the risks, e.g. theft from a garage, continue to be covered under certain circumstances, depending on the insurer, and mostly for a limited period of time. Some insurers grant a suspension discount not only on liability and full casco insurance (comprehensive and collision) but also on partial casco insurance (only comprehensive). You can find more detailed information in your General Insurance Conditions.
As soon as you use the number plates again, your insurer grants you a discount calculated pro rata temporis, deducting the administrative fees. Certain insurers already offer the discount when the number plates are deposited, thus enabling you to change insurers.
In order to save themselves and policyholders administrative work and expenses, most insurance companies offer whole-year premiums for motorcycle insurance; i.e. suspension is waived. This model makes it needless to deposit the number plates for a few weeks/months in winter.
The effort of depositing number plates during the winter season hardly pays off with motorcycle insurance – in contrast to car insurance, where the suspension discount amounts to considerably more. Ask your insurance provider to find out how high your suspension discount would be and what administrative costs will be deducted. That way you can estimate if it is worth suspending your insurance for the desired period of time in your case.