This badger stamp is from a series of "The Red Book of Mammals of Belarus" which is a collection of animals that are rare and/or endangered. The book is updated every 10 years with the latest edition being in 2015. Badgers have been on the endangered list for 25 years.
The M on the stamp designates it as airmail postcard abroad.
for the letter B - Belarus, badger (barsuk in Russian)