ClearSign Technologies (CLIR) - 2021 Q1 - Quarterly Report

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q (Mark One) x QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended March 31, 2021 OR ¨ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from ______________ to _______________ Commission File Number 001-35521 CLEARSIGN TECHNOLOGIES CORPORATION (Exact name of registrant as specified in its charter) W ...