ClearSign Technologies Corp

SCHEDULE 14A

(RULE 14a-101)

INFORMATION REQUIRED IN PROXY STATEMENT

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

(Amendment No. )

Filed by the Registrant ⌧

Filed by a Party other than the Registrant¨

Check the appropriate box:

(Name of Registrant as Specified in Its Charter)

(Name of Person(s) Filing Proxy Statement, if Other Than the Registrant)

Payment of Filing Fee (Check the appropriate box):

8023 E. 63rd** Place, Suite 101**

Tulsa, Oklahoma 74133

Dear Stockholder:

You are invited to attend the 2025 annual meeting of stockholders (the “Annual Meeting”) of ClearSign Technologies Corporation (the “Company,” “we,” “us” or “our”) on July 25, 2025 at 1:00 p.m. Central Daylight Standard Time. The Annual Meeting will be completely virtual conducted live via the Internet. You will be able to attend the Annual Meeting online and submit your questions during the Annual Meeting by visiting www.virtualshareholdermeeting.com/CLIR2025.

At this year’s meeting, you will be asked to vote on: (1) the election of six members of our board of directors to serve until the next annual meeting of stockholders or until their respective successors have been elected and qualified; (2) the approval, on an advisory basis, of the appointment of BPM CPA LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2025; and (3) the approval, on an advisory basis, of the compensation paid to our named executive officers.

Our board of directors (the “Board”) has fixed the close of business on May 29, 2025 as the record date for determining the stockholders entitled to notice of and to vote at the Annual Meeting and any adjournment and postponements thereof (the “Record Date”).

Please use this opportunity to take part in the affairs of the Company by voting on the business to come before this meeting. If you are a record holder of the Company’s common stock on the Record Date, you are eligible to vote with respect to these matters either electronically, at the meeting, or by proxy. It is important that your shares be voted, whether or not you plan to attend the meeting, to ensure the presence of a quorum. We urge you to authorize your proxy in advance by following the instructions printed on it. Returning the proxy does not deprive you of your right to attend the virtual meeting and vote your shares.

Sincerely,

/s/ Colin James Deller

Colin James Deller, Chief Executive Officer

Tulsa, Oklahoma

June 13, 2025

IMPORTANT NOTICE REGARDING THE AVAILABILITY OF PROXY MATERIALS FOR THE STOCKHOLDER MEETING TO BE HELD ON JULY 25, 2025; THIS PROXY STATEMENT AND THE 2024 ANNUAL REPORT ON FORM 10-K ARE AVAILABLE AT WWW.PROXYVOTE.COM

8023 E. 63rd** Place Suite 101**

Tulsa, Oklahoma 74133

Notice of 2025 Annual Meeting of Stockholders

to be held July 25, 2025

To the Stockholders of ClearSign Technologies Corporation:

The 2025 annual meeting of stockholders (the “Annual Meeting”) will be held at 1:00 p.m. Central Daylight Standard Time on July 25, 2025. The Annual Meeting will be a virtual meeting of stockholders conducted live via the Internet. You will be able to attend the Annual Meeting online by visiting www.virtualshareholdermeeting.com/CLIR2025. During the Annual Meeting, stockholders will be asked to vote either directly or by proxy on the following matters discussed herein:

If you are a stockholder of record as of May 29,2025, you may vote at the Annual Meeting as further described in the accompanying proxy statement. The Notice of Internet Availability of Proxy Materials (“Notice of Internet Availability”), proxy statement and form of proxy are being distributed and made available on the Internet on or about June 13, 2025.

Your vote will be especially important this year. Jeffrey Feinglas submitted documents to the Company purporting to provide qualifying and timely notice (the “Purported Feinglas Notice”) of an intent to nominate two director candidates (the “Purported Feinglas Nominees”) for election to the Board at the Annual Meeting. The Company has informed Mr. Feinglas that the Purported Feinglas Notice is invalid due to its failure to comply with the Company’s Bylaws (the “Bylaws”) as a result of material omissions and other material deficiencies.

Accordingly, any director nominations made by Mr. Feinglas will be disregarded, and no proxies voted in favor of the Purported Feinglas Nominees will be recognized or tabulated at the Annual Meeting. As the Purported Feinglas Notice will not be recognized as valid under Delaware law, unless otherwise so determined by a court, the Company will not include the names of the Purported Feinglas Nominees on a “universal proxy card.”

However, if litigation occurs and the result of such litigation is that the Purported Feinglas Notice is deemed valid and a court of competent jurisdiction determines that Mr. Feinglas complied with the Bylaws and with Rule 14a-19 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), then the Company would amend the proxy statement and the accompanyingWHITEproxy card to reflect that development to comply with the applicable aspects of Schedule 14A and Rule 14a-19 of the Exchange Act. Further, in such scenario, the Company would include the names of the Purported Feinglas Nominees on a “universal proxy card” and mail a revised proxy statement and such universal proxy card to stockholders.

In addition, in the above scenario, no proxies or votes received on the Company’s previously circulated proxy card would be recognized or tabulated at the Annual Meeting. These proxies would be disregarded. Accordingly, if you vote on the Company’sWHITEproxy card accompanying the proxy statement and the Purported Feinglas Notice is subsequently deemed valid and Mr. Feinglas is found to have subsequently complied with Rule 14a-19 of the Exchange Act, then your votes would not be recognized or tabulated and you would have to vote again for your vote to be counted. In such scenario, the Company would potentially need to delay the Annual Meeting to allow time for stockholders to

receive and consider the new proxy materials.However, there is currently no litigation pending related to the Purported Feinglas Notice or any circumstances related to the Purported Feinglas Notice.

Despite the Board’s determination that the Purported Feinglas Notice is invalid, you might receive solicitation materials from Mr. Feinglas, including proxy statements and proxy cards.WE URGE YOU TO VOTE ONLY ON THE WHITE PROXY CARD FOR THE BOARD’S PROPOSED DIRECTOR NOMINEES, TO DISREGARD ANY MATERIALS SENT TO YOU BY, OR ON BEHALF OF, MR. FEINGLAS, AND TO NOT SIGN, RETURN OR VOTE ANY PROXY CARD SENT TO YOU BY, OR ON BEHALF OF, MR. FEINGLAS. We are not responsible for the accuracy of any information provided by or relating to Mr. Feinglas or the Purported Feinglas Nominees contained in any proxy solicitation materials filed or disseminated by, or on behalf of, Mr. Feinglas or any other statements that Mr. Feinglas or his respective representatives have made or may otherwise make.

The Board recommends that you vote“FOR”** the Board**’s proposed director nominees —Judith S. Schrecker, Catharine M. de Lacy, G. Todd Silva, Colin James Deller, Anthony DiGiandomenico and Louis J. Basenese.

Dated: June 13, 2025

By order of the Board of Directors

/s/ Brent Hinds

Brent Hinds

Chief Financial Officer​

Whether or not you expect to attend the Annual Meeting, please vote at your earliest convenience by following the instructions in the Notice of Internet Availability or the WHITE proxy card you received in the mail.