No, it's not - it's a box with an X through it (as per msiegel's post), to indicate the Clear function.
It's a pretty rounded "box". My French Canadian AEK has a square box with an X through it - and it doesn't look like infinity. It's definitely the "Clear" function, but on my other four old Mac keyboards, it just says "clear".
(I assume you press the "suppr" button when you want your supper and the "aide" button if you've got AIDS.)
Edit: Now that I've looked at the pictures again, I see the symbols are the same. OK, no infinity then. (I'm infinitely disappointed)