Hello,
Thanks a lot for all the input.
It looks like there is no industry-recognized certification of such a kind. Could be a semi-business idea for FSFE educational stream to provide certificates of such a kind.
Of course, no certificates really guarantee anything. It's just an entry level. But it is sometimes useful approach to require certificates in a big organizations. E.g., to request subcontractors in Bangalore to have certain amount of "OSS certified" persons in the team. At least they will know the very basic things about licensing and OSS.