I had till now assumed this label was somehow attached to Walther Glas, probably because of all the solifleurs I found it on (and their sellers all saying these were Walther), but after Dirk cast some doubt on that, while researching it further I found an ebay entry with the same style label, but with the letters DK instead of MG. Now I really have to find out what is going on with that label.
Wild speculation: could it perhaps be some sort of export label, with the MG standing for Made in Germany, and the DK indicating Denmark? Or some cooperative label where more than one glashütte is involved with?
The vases I've seen them on (a few examples attached) all look quite 60s - 70s.
The DK version of the label can be found here: http://cgi.ebay.de/Glas-Vase-Etikett-Handgearbeitet-Mundgeblasen-DK-/120610377892
I kindly asked the seller if he would be prepared to send me a close up picture of the DK version of the label. If he agrees, I'll post it here.
And of course one of my solifleurs inclused, with label close up. Detail: all the MG solifleurs I have with this label look slightly dented at the rim. I have four different ones so far, a red and orange one that clearly belong to the same series, and two clear ones slightly heartshaped with a pattern of stripes that I forgot to make a photo of so far...