I never noticed it before, but when you see the two cards together, it seems to pop out...
....the sleeve patch.
So what is it? It's not this...
....the sleeve patch the Cubs wore starting in 1962. It's just a picture of a mitt. Why are they wearing a mitt?
In fact, why are the other teams wearing a mitt, too?
(actually, I'm assuming all the other NL teams wore it, though I couldn't find a card with a Phillie wearing one).
The answer....The National League was celebrating it's 75th anniversary in 1951 and all the teams wore this commemorative patch. There's no writing on the patch, no National League symbol; just a glove. It seems kinda plain, but I guess times were simpler back then.
As it turns out, the National League has worn anniversary patches a couple other times too. I'll have that in a few days.