Meaning of hash symbol in pin name
I suppose it means active-low logic, usually indicated by an overscore. Signals like WE#, CE#, LB# and UB# are typically active-low. In datasheets you'll see them as \$\overline{\mathrm{WE}}\$, \$\overline{\mathrm{CE}}\$, \$\overline{\mathrm{LB}}\$ and \$\overline{\mathrm{UB}}\$.