It signifies that either a foreigner or recent immigrant, or perhaps a dyslectic or anyone who would like it to appear as if a foreigner or recent immigrant or a dyslectic wrote the note.
Verily the poorly-skilled can never write better, and the better never poorer.
But are there known 'kidnap ransomers' that could be deduced through language? It seems unlikely, I guess, unless Norway has enough local variances that would give a native speaker away through dialect.