Pinko is a slur used to describe Russians in a derogatory way. Originally referred to Communist sympathizers - later as a general slur against all Leftists, including Communist Party members. Now pretty much synonymous with Russians/Communists.
The word Pinko is a racial slur that has been used historically to degrade and dehumanize russians. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to russians. If you are unsure about whether or not it is appropriate to use the word Pinko, it is best to err on the side of caution and avoid using it in any situation.