If after contacting the campus police, you cannot find the original owner...I would probably take it. Considering how long it's been there...it's likley the owner has graduated etc...
And as far as bikes in the trash...... it's been many years, but I got two older bikes from the trash/dumpster this way. Fixed them up and enjoyed many miles of happy riding on something that someone else discraded and would have ended up in a landfill somewhere. When I finally did get rid of them, I GAVE THEM AWAY to friends and made no money on them.
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Just Do It..