Yea, I had posted a topic on this a while back, because I bought a large store sign that said Balboa, and then I started seeing the label all over.
In my searches I came up with this site too - There is Art Glass Association of Southern California Glass Guild at Balboa Park, San Diego - but they have nothing to do with Italian glass, they are a cooperative of artists that live/work in Balboa Park San Diego. I emailed them to see if it had anything to do with the Balboa labels I found in my Murano pieces, but they replied that they had nothing to do with that. Also had no idea about the labels or any history connected with San Diego.
I have found the label in Fratelli Toso pieces, as well as Barovier and Seguso pieces recently. At first I thought it was only pieces by Toso that had the label but more and more pieces by other makers are appearing with the same label.
I also do not know the exact dates the label was in use, but by the pieces I have I would say the 50's - 60's seems accurate, and maybe earlier. Not sure though.
I will post the photo of the store sign I have (in the shape of a Fish), which I do not know who made it, but looks like a very special piece. If anyone has any documentation of the company, or catalogues, specific dates that can shed some light, that would be excellent! That would clear up many questions we ALL have right now. I know i've been very frustrated by the lack of info, lol. We need to crack this one!