I remembered thinking about this when reading another thread about pull ups but I didn't want to steal someone elses thread.
I don't know about other gyms, but my student rec center doesn't have an actually pull up bar (that I know of) However, they do have these things:
Is it better to use the slanted bars or the bars that would have the palms facing inward?
In case anyone is wondering, I didn't actually take this picture, I found it on the website.