They could start by removing them from tame rides that are extremely unlikely to trigger any health conditions that are listed out of mere routine. Their sheer prevalence is a large part of why they usually go ignored. But in order to be truly effective, at least for those willing to read them, more detail is required. Of course, if you have novel-length signs posted outside every ride, that creates its own problems in terms of the likelihood of guests paying heed to them. But as of now, they only act as protection from litigation, not as a valuable resource to guests.