I had a full single life (maybe too rich - led me to be a bit too caddish for too long and to get married very late) vis a vis young ladies so I am not a prude by any means. However, I do not think what they wrote and displayed is just "fun" or funny. The fact is that in many case (not all) young men in college (and otherwise) view the boundaries of partying and the mating ritual very differently and young ladies, particularly when drinking too much (and yes I know it's their fault for doing so) can be very vulnerable to the aggressive advances of young men, particularly where they don't want to be seen as "prudes" or not cool. Of course if young ladies (like many young men) want to be promiscuous, that's up to them.
What is reflected on the banner and, more so, in the fact that they felt comfortable enough to display it, is a perfect example of the mentality that leads guys to thoughtlessly seek to engage in non-consensual sexual activity with young ladies which often has very destructive consequences to the young ladies involved. So I think addressing the banner to show that approaches like that, even jokingly, should not be the norm among young men who ascribe to be gentlemen, is the right way to go and referring to it as PC or something like that misses the point. The mentality that fosters banners like that and a hundred examples of other similarly offensive utterances (whether sororities do it as well or not - and if they do, shame on them) is simply wrong and one of the ostensible things that college is supposed to teach young people - I would think - is the difference between right and wrong.