Surely there is no such thing as "the most failsafe"...
Something either fails safe or it doesn't.
If no ETOPS signage = no flight then any failure to provide the required signage would result in a safe condition, i.e. no flight!
Of course, the presence of signage alone could never ensure that any required human processes, such as checks and maintenance, had been completed. Which is why signage should only really be relied upon as an additional layer of protection.