I grant that the second cursive letter is difficult to identify, it doesn't look like how I would write any of the possibilities: P, T, S or L, but then that "G" isn't something my third-grade teacher would have given a passing grade to, either.
I'm still in the "Giovanni Papillardo de Milano" camp, until somebody can verify that some other company made the "San Marco" posts.
Just for more comparison, here's what one of the vintage 3TTT posts looked like (no family relation to any of the "G. P." posts I've seen)