Most of the Magnor artglass from the 50/60'ies wasn't signed by the artist or with a company mark.
There are examples of the crude "Magnor" inscription, which weren't, as far as I know, put there by policy.
More likely the piece was marked by someone at the factory or an outlet.
The crude incision mark is mentioned in "Moderne Antikviteter II" by Astrid Olsen published in 2002
and I also have a small candydish with this mark, cost a whopping 80 pence
Magnor artglass was signed with a paper label until the 70'ies.
The factory was started as an offshoot of swedish Eda in response to new trade rules between the
two countries.
I don't know if they mark their seconds, but they'll probably reply to an email inquery.
By the by - most norwegians speak and write reasonable english so emailing any norwegian
maker in english shouldn't be a prob.