my sim moved and left university poster board behind...

Once my sim enrolled to uni and she didn't receive the board at all. E-mailing the professor about progress didn't give the board in my sim's inventory. Unfortunately even though my sim studied and did all the homeworks and everything right she got F. So good luck with that.
Anyway, maybe you could try to visit the place where your sim moved from and get it back. I think there should be an option to put it in inventory since your sim is the owner of that board. If nobody lives there now you can move in some random townie in order to make it "visitable".