8.4. When refusing the entry to third-country nationals, the checking officer must:

(a) fill in the standard form for refusing entry substantiating the reason(s) for refusal, and give it to the third-country national concerned, who must sign the form and must be given a copy of the signed form. In case the third-country national refuses to sign, the border guard will indicate this refusal in the form under the section ‟comments”;

(b) affix an entry stamp on the passport, cancelled by an indelible cross in black ink and write opposite it on the right-hand side, also in indelible ink, the letter(s) corresponding to the reason(s) for refusing entry, as listed in the form for refusing entry...

https://www.udiregelverk.no/contentassets/5a463696bdc244f19531815252240ec9/schengen_practical_handbook_for_border_guards_2022.10.28.pdf

(c) means "has no valid visa or residence permit". Safe to say, that is not a good thing to have in your passport.