can a massage business legally put up a gratuity sign
It depends what a gratuity sign is, and what it says.
As a Franchise Attorney I agree with the other attorney answer. By a gratuity sign, do you mean one that simply encourages tips? Consult with a good business or franchise attorney in your area for specific advice.
Mr. Franchise - Kevin B. Murphy, B.S., M.B.A., J.D.
Franchise Foundations, a Professional Corporation