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                                                                     Exhibit 4.3

                             SUPPLEMENTAL INDENTURE

     This Supplemental Indenture dated as of February 12, 1999, between
FirstMerit Corporation, an Ohio Corporation (hereinafter the "Surviving
Corporation"), and Firstar Bank Milwaukee, National Association, successor via
merger to Firstar Trust Company, a national bank, as debenture trustee
(hereinafter the "Debenture Trustee").

     WHEREAS, Signal Corp (fka FirstFederal Financial Services Corp), an Ohio
corporation (hereinafter the "Merging Corporation") entered into an Indenture
dated as of February 13, 1998 with the Debenture Trustee (hereinafter the
"Indenture") for the purpose of issuing 8.67% Junior Subordinated Deferrable
Interest Debentures due February 28, 2028 (the "Securities"); and

     WHEREAS, the Surviving Corporation has agreed to assume the Indenture
pursuant to Section 2.8 of the Merger Agreement; and

     WHEREAS, Section 10.01 of the Indenture permits the Merging Corporation to
consolidate or merger with another Person provided the terms and conditions of
this Section 10.01 are met.

     NOW, THEREFORE, in consideration of the premises and mutual agreements
herein contained, the parties agree as follows:

     1. SURVIVING CORPORATION. The Surviving Corporation hereby represents and
warrants that it is a corporation organized and existing under the laws of the
State of Ohio.

     2. ASSUMPTION OF INDENTURE. The Surviving Corporation expressly assumes the
due and punctual payment of the principal of (and premium, if any) and interest
on the Securities according to their tenor and the due and punctual performance
and observance of all the covenants and conditions of the Indenture which were
to be kept and performed by the Merging Corporation, and shall be deemed a party
to such Indenture as if an original signatory thereto.

     3. ACCEPTED BY DEBENTURE TRUSTEE. The Debenture Trustee accepts this
Supplemental Indenture as satisfactory in form as required by Section 10.01 of
the Indenture.

     4. NAME. The Trustee and Surviving Corporation agree that the Indenture is
hereby amended such that the words "FirstFederal Services Corp" are replaced
with "FirstMerit Corporation" wherever such words appear in the Indenture.

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     5. CAPITALIZED TERMS. Each capitalized term used but not defined herein
shall have the meaning ascribed thereto in the Indenture.

     Except as expressly amended hereby, the Indenture shall continue in full
force and effect in accordance with the provisions thereof and the Indenture is
in all respects hereby ratified and confirmed. This supplemental indenture and
all its provisions shall be deemed a part of the Indenture in the Manner and to
the extent herein and therein provided.

     IN WITNESS WHEREOF, the parties hereto have caused their names to be signed
hereto by their respective officer thereunto duly authorized as of the day and
year written above.


                                 SURVIVING CORPORATION:

                                 FIRSTMERIT CORPORATION,
                                 an Ohio corporation

                                 By: /s/ Austin J. Mulhern
                                    ------------------------------------
                                 Its: Senior Vice President, Finance and
                                     -----------------------------------
                                      Administration

                                 DEBENTURE TRUSTEE:

                                 FIRSTAR BANK MILWAUKEE, NATIONAL ASSOCIATION,
                                 a national bank

                                 By: /s/ Yvonne Sira
                                    ------------------------------------
                                 Its: Assistant Vice President
                                    ------------------------------------

                                 ATTEST:
                                 /s/ Charles R. Fiderson
                                 ---------------------------------------
                                 Charles R. Fiderson
                                 Assistant Secretary
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