Legaly yes you may. the Theater may have a sign posted that says No Weapons, and that is the choice of the management/company. They can ask you to leave if by some odd chance you are found out? and at the worse have you tresspassed if you wont leave.
There is a movie theater in Pinellas county, on E. Bay just west of US Hwy 19 N. that I went to one time. I did not see the No Weapons sign in the window when I went. I did see it on the way out, and I promptly went to the car, retrieved a No Gun, No money card and handed it to the manager in charge.
He mentioned that the sign was in place because of corporate office, and he had no control over it. I told him I would not be coming back until the sign was removed. He told me he was sorry and that he wished he could do something but his hands were tied.