shabbat

Question

there is a well known retail chain store in and around nyc that has a sign posted on the window. they are open on shabbat and yom tov. the sign reads something like this. "we comply with shulhan aruch 245 with regards to opening on shabbat..." i read it and dont quite understand it . it mentions something about a partnership. can you explain a bit? also. if it is ok why doesnt everybody do it?