"Chip Select Bar" - proper jargon or a place to have some beers at?
There's no "standard" way of representing an active-low signal.  I have seen various combinations of: \$\overline{CS}\$, \$nCS\$, \$!CS\$, \$CS\#\$, \$\_CS\$, \$CSB\$, etc.  All of them mean the same thing "Active-Low Chip Select". Myself I prefer to use \$\overline{CS}\$ given the choice, or if the typesetting software won't allow it (I use \$\LaTeX\$ for all my datasheet typesetting so it does allow it) then \$CS\#\$. But it tends to be largely a matter of personal choice, what someone was taught at university, or maybe even regional conventions (I notice a number of the search results are for German sites).  

I've never seen the word Bar spelled out before either though, but in a textual context it does make a certain amount of sense if you can't do a real bar, since you could say "See Ess Bar" in speech.