...but I have no evidence that they are really signed because GSV is out-dated (older than Rv/Fv changes). However, if other Rv routes are indicated on vegvesen.no and GSV from 2016 is available, I could always find signs. If that's not enough, we should keep this thread open till GSV is updated.
Rv451https://www.vegvesen.no/vegkart/vegkart/#kartlag:geodata/vegreferanse:94115.569824439:6472242.3699647/@94435,6472878,14https://no.wikipedia.org/wiki/Riksvei_451GSV is from 2009/10, no signs found
Rv681https://no.wikipedia.org/wiki/Riksvei_681https://www.vegvesen.no/vegkart/vegkart/#kartlag:geodata/vegreferanse:137920.58615653:7018079.4611986/@137733,7018308,14GSV is from 2012, no signs found
Rv833https://no.wikipedia.org/wiki/Riksvei_833https://www.vegvesen.no/vegkart/vegkart/#kartlag:geodata/vegreferanse:569356.25788205:7598600.7972414/@569410,7598700,16GSV is from 2010, no signs found
Rv881https://no.wikipedia.org/wiki/Riksvei_881https://www.vegvesen.no/vegkart/vegkart/#kartlag:geodata/vegreferanse:818316.011354:7784299.3470796/@818175,7784985,16GSV is from 2010, no signs found