I'd talk to the building owner and find out what they'll allow, then do as much as you can. You might be able to have a basic sign up during normal hours, but when you're open make more of an entry way to the haunt that spills out into the sidewalk. You might even be able to have your ticket booth outside, which would help save on space inside and helps draw attention outside. If you're limited to just a sign, I'd get the best 3D sign above the door as you can (which can be expensive unless you foam carve it) and dress up the windows.
Fear Town Haunted House