Thin lines making up a blurry text, not something I recall ever seeing on any old marble bags but believe I have seen on fantasy bags. Al knows his bags for sure. But a quote from the "realorrepro" site, "Low resolution digital images can often be identified by jagged, angular or ragged edges on letters and art work (Fig. 12) Any of those features indicate a new header."
Things to look at on this bag to indicate that it's a fantasy bags are more than one or two colors (this has 3), No seam down the middle, and incorrect product placement. This is a teens through 30s or 40s logo on a poly bag, which wasn't popular until the 50s-60s and after and even then it was with a seam down the back. I don't think Mastermobile was a product after the 50s anymore, so there is barely any overlap. Also, fantasy bags normally have round wire staples, which yours has, not flat.
Also look at the border around the edges, this is common on older repro bags, along with the size and proportions of the header, which seems to be common during that time. Also across the bottom shows perforations, meaning this was a roll product of tear-off bags, blown poly tube construction which wasn't a method of production during the 50s. They were still folding the plastic into a tube and melting it (which makes the seam on the back) during that time.
Compare with the info and photos here and you'll see the similarities: https://www.realorrepro.com/article/Fake-and-fantasy-bags-of-marbles