Just to expand, I've never heard of an engineer from the wrong field signing off on a document (e.g. an EE signing off on a structure), but here's a lesser example of unskilled practice and the corresponding disciplinary action: https://www.apega.ca/assets/PDFs/discipline-decisions/18-011...
It takes ~8 years to fulfill the requirements to acquire a professional license. It's not worth the risk of being caught.