I have a situation and need help - all commercial lenders have recently moved to a building of their own - not in a branch - and on a rare occasion believe they may accept a deposit from one of their customers to save the customer a trip to a branch. The deposits could be for personal accounts.

Do I need to place FDIC member signs and funds availability in this building? They won't "regularly or routinely" accept deposits but MAY if asked.

I think signage is the least of your worries. What you have described constitutes branch banking under Federal and most State laws that I know of. I would be more concerned with operating a branch without a branch charter.