pin (verb), slang, meaning 'to see or watch.'

I understood it to mean "to see" in the sense of the date exclusively; "going steady". Lyrics from Bye, Bye Birdie, the musical and film from that period:

-Have you heard about Hugo and Kim?
Did they really get pinned?
Did she kiss him and cry?
Did he pin the pin on?
Or was he too shy?
Well, I heard they got pinned
-Yeah! Yeah!
I was hopin' they would!
- Oho!
Now they're livin' at last,
Goin' steady for good!

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