help with RAF WW2 record

I’m doing some Family History and on the service record it mentions the term-

SB2
It is stamped on an RAF Service record from 1944 but Air Historical Branch at Northolt don’t have an idea. It appears twice, once under Special Qualifications and again under Good Conduct Badges.
Can anyone throw any light on what SB2 means?

The Air Historical branch at Northolt can’t help.

Any help appreciated.
Graham Morley