PE certification and applying PE's seal

Except as provided in 40 CFR §112.6 for qualified facilities, a Professional Engineer (PE) must certify a facility’s SPCC Plan.  In order to certify an SPCC plan, must a PE apply his seal to the plan, or is the PE’s signature on a certification statement sufficient for SPCC purposes?

For the PE certification to be effective for SPCC purposes, this certification must be completed in accordance with the law of the state in which the PE is working.  Some states require a PE to apply his seal to effectuate a certification; others do not.