ECN Forum Forums Code Related Discussion Canadian Electrical Code Topics 347 v marking on cover plate.

I would say no. There is no reference to it in the code book.
It is good practice to install a cover that says 347 though, it gives a heads up to whoever is working on it.

They make stainless steel flush switch covers that have 347 stamped on them and I think that they make them for FS boxes as well. I don't think that they make them for regular surface mounted boxes though.