The Day Span and Nail is the beauty salon in which James McGill rents an office in the back shop in Better Call Saul.

Not having the means to rent an apartment, Jimmy installed a sofa bed in his office in order to be able to sleep there. ("Uno")

It is not currently know if it is the same beauty salon that Saul proposes to Jesse and then Walter to launder their money in Breaking Bad. This does not seem to be the case, especially since the managers are different.