Ah interesting Essi thanks. I can definitely confirm that your vase is a Jaako Niemi design as I collect his stuff

however my guess would be that someone other than the good folks at Nuutajarvi put that FK on. I have, in the course of collecting for many years, seen an amazing variety of forged, faked scatched out and added to signatures on vases, and that one looks to be one of the later made ones that didn't have the designer name, just the nuutajarvi notsjo like this one, also a Niemi design
http://www.ebay.com/itm/Vintage-Finland-NUUTAJARVI-NOTSJO-Scandinavian-Art-Modern-Glass-Bowl-/151464574032?pt=LH_DefaultDomain_0&hash=item2343fdfc50I had posted this question on the Design Lassi sight a few years ago and for some reason the reply wouldnt show up till i just now did a google search for it lol. heres a reply I received:
Nuutajärven tehtaan vuoden 1953 kuvastossa olevat ohuet kaiverretut maljat ja vaasit ovat Rista-sarjaa, mallien suunnittelijaksi mainitaan Kaj Franck.
Koristekaiverruksia esineissä oli runsaasti erilaisia, mm Kaj Franckin ja Hilkka-Liisa Aholan käsialaa.
Esineitä tehtiin runsaasti mm USA:n vientiin ja niiden signeerauksissa käytettiin erikoisempaa tapaa: Notsjoe FK, mikä tarkoitti Notsjö eli Nuutajärvi. Ja FK tarkoitti Kaj Franck (ei siis Friedl Kjellberg). Franck ei halunnut käyttää noissa esineissä omia nimikirjaimiaan KF, koska hänen mielestään hennot ja koristekaiverretut esineet olivat liian koristeellisia hänen pelkistettyyn makuunsa.
Esineitä myytiin ulkomaille paljon ja niitä näkee usein mm Ebayn huudoissa USA:ssa.
i can only do a somewhat suspect google translation but it gives the gist:
Iittala factory in the 1953 catalog of fine carved bowls and vases are Rista-series models of designer Kaj Franck is mentioned.
Decorative engravings of a great variety of articles, such as Kaj Franck, and Hilkka-Liisa Ahola's handwriting.
Objects were plenty of such US exports and their signature, was used as an extra special way: Notsjoe FK, which meant Notsjö a Nuutajarvi. FK meant Kaj Franck (ie not Friedl Kjellberg). Franck did not want to use those articles in your own initials KF, because he felt delicate and koristekaiverretut objects were too fancy for his minimalist liking.
Objects were sold abroad a lot and they can often be seen for example Ebay screams of the United States.
the one I pictured is
In Nuutajärvi(Notsjö) cataloque 1953. Engraved and plain glass: Vase 125mm, number H 415
Name: "Lotus", no designer in cataloque.