What did the sign say?
If it was a typical Ohio gunbuster sign, you may not carry. It is supposed to be posted conspicuously, but the lack of conspicuousness will only be a defense against a trespassing charge for someone who does not know it is there. You know it is there. Do not carry in that store.
Contact corporate. Local management may be violating corporate policy. If corporate policy does not allow carry, respect their choice. I respect that choice by my lack of patronage.