 SEATTLE, June 7, 2021 PRNewswire -- ClearSign Technologies Corporation Nasdaq: CLIR ClearSign or the Company, is set to join the Russell Microcap Index at the conclusion of the 2021 Russell indexes annual reconstitution, effective after the US market opens on June 28, according to a preliminary list of additions posted June 4. Membership in the Russell Microcap Index, which remains in place for one year, means automatic inclusion in the appropriate growth and value style indexes. 