Looks to me like your purple "SAN FRANCISCO" flag likely
did fly on the Wrigley scoreboard mast. It appears to have a pair of D-rings affixed to the spine. Additionally, the fish tail-end is very tattered--evidence that it withstood some serious wind only the "windy city" could produce.
If you look at the scoreboard photo above, you can see evidence of these D-rings in the photo. Between the first place Dodger flag, and the second place Giant flag (had to slip that in there
), note the break in the white spines. This is where the two D-rings would have been linked together. In order to link flags together like this, you gotta use D-rings over the more conventional grommet, which would tear apart pretty quickly.
Your "GIANTS" flag could
not have come from the Wrigley scoreboard mast as it appears to have a pair of grommets on its spine. It certainly could have come from the rooftop, however.
What are the dimensions of the two flags? It looks like both measure about the same height. If it was a modern flag, the purple flag should measure 2.5' tall. But, it looks like it may be 30+ years old. So, I'm not sure if the dimensions the manufacturer gave me were the same back in those days....