N.Y. Tax Law § 254
Whenever any mortgage other than a mortgage specified in section two hundred and sixty-four has been recorded prior to July first, nineteen hundred and six, the record owner thereof may file with the recording officer of the county in which the real property, or any part thereof, on which said mortgage is a lien, is situated, a written statement under oath verified by the record owner or the agent or officer of such record owner describing such mortgage by giving the date of the same and the liber and page of the record thereof together with the names of the parties thereto, specifying the amount then remaining unpaid on the debt or obligation secured thereby, and electing that it shall become subject to the tax prescribed by section two hundred and fifty-three of this chapter. Whenever any unrecorded mortgage has been executed and delivered prior to July first, nineteen hundred and six, the owner thereof may record the same upon filing with the recording officer a similar statement and paying the tax as herein prescribed. A tax shall thereupon be computed, levied and collected upon the amount of the principal debt or obligation unpaid at the time of the filing of such statement, or of the recording of such mortgage and filing of such statement. On the payment of such tax as herein provided, the recording officer shall note on the margin of the record of such mortgage the fact of such statement and of the amount of the tax paid, attested by his signature, whereupon such mortgage and the debt or obligation secured thereby shall be entitled to the exemptions and immunities conferred by this article, and all of the provisions of this article shall thereafter be applicable to said mortgage. Whenever the original mortgage is presented to the clerk together with the statement he shall also note on said original mortgage the fact of the filing of the said statement and also the amount of the tax paid duly attested by his signature, which indorsement shall be conclusive evidence of the payment of such tax.
N.Y. Tax Law § 254