(not asking for advice, just a thought that popped into my head)

I understand that medical injuries are a factor in something like a missing caution sign, but how is it that someone can sue and win in a case of common sense when a company has no sign? For example, many companies use signs so they are not liable for theft at say a public laundromat but some don’t have this. How do they avoid a lawsuit when they don’t have a sign even though it is common sense? What type of law protects a customer when a business lacks a sign and allows them to win against a business owner?