Perplexing. Tag looks older than 1958, but the style of pennant matches another one the same seller had with "SF Giants" embroidered in like fashion.
The Giants didn't start wearing the Orange/Black motif until 1933, so that's the very oldest it could be. Of course, the pennant could be a generic Giants pennant, with no affiliation whatsoever to the MLB club. I don't think that's the case, but would vote 1950s on this one... simply because that's the era that fits best with the black/orange combination. The Giants wore black and orange that entire decade, and seller had very similar pennant with "SF" embroidered on.
Preponderance of evidence says 1950s. Might be New York / might be SF. There's always some guesswork with these generic style pennants. I don't love the generics, but if I had every other Giants pennant known to mankind, I might pursue it
Also, there are actually quite a few subtle differences between the two tags, if you look closely at in the Spalding logo font.