I'm not sure but i think this label is to commemorate 10th anniversary of the first airmail flight between
Helsinki-Stockholm. I found some information on that.
The Helsinki-Stockholm flights opened on June 2, 1924. Judging from a
circular by the Post and Telegraph Administration, however, the first mail flight
did not happen until June 28. The mail flights to Sweden continued every
weekday until August 26, in co-operation with the newly founded Swedish
airline company, A/B Aerotransport. (Eino Fjällström, “Lentopostin alkuvaiheet Suomessa” (The beginning of airmail in Finland)).
Year: 1934, Gummed. Günter Mair's catalogue no: - SWE-C-5, imperforated, dark blue/yellow, 4****