In 1955 in Italy, "Vicenza A.C." played in "Serie A" showing a blue "R" which was the logo of "Lanerossi" textile factory. Team changed also its name in "Lanerossi Vicenza A.C." and played 20 seasons at high levels in Serie A. That's considered the first time that a team was sponsored in Italy, but I don't know if it was first time in the world. You can read something about Lanerossi Vicenza here:
it.wikipedia.org/wiki/Lanerossi_Vicenza#La_prima_sponsorizzazione_in_Italia
(It's in Italian, sorry... you can translate it in your language with google or something similar)