At most conferences, the sign above might provoke a moment of puzzlement. But this is the JMM, the Joint Mathematics Meetings, being held this year in New Orleans. As far as I can tell, the 5,400 mathematicians gathered here are quite untroubled by these instructions. And after all, they know perfectly well that a whole uncountable continuum lies between floors 2 and 3.
Onward and upward, indeed. And downward. And everything in between.