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are you supposed to e-mail the prof or anything just acknowledging that you received news you booked his class/were excited to hear? or no? thanks. the class was an uncurved ~40 person class if that matters.

This sounds ... weird. And unnecessary. The prof will know you booked the class because he/she gave you the grade. It's not like you won a Nobel prize or something.

No.

You're supposed to put notice of the award on a sandwich board and wear it around school for three weeks.

I would say this is ok only if it comes up organically. Profs may not necessarily know who it was though, with blind grading and all.

For example, I got a book award in my writing class. After our final paper was returned, it was mathematically obvious I was going to get it. Before grades were posted, my professor sent an email to the effect, "as you received the highest grade on the final paper, you've also booked the class. Congrats." Then saying "thanks" is cool.

Or like where you have a class like contracts that spans two semesters - once had a professor ask me if I booked his class first semester. I hadn't, but if I had I'd have just been like, "yeah, thanks I like the class" or something.

But spontaneous, unprompted? Probably not normal.