Exactly correct. Also, you cell phone will not interfere with medical equipment. In fact, nurses in intensive care use one or more radio devices (like Vocera) to be in constant communication, and ICU's are about as intensive a location for medical equipment as you will get outside the OR. Years ago it may have been the case, but the concern was mostly out of fear. The signs are likely still posted for legal reasons than anything else - if they took the signs down it could be considered that they were "endorsing" cell phone use. Enter a lawyer looking for money and an unhappy patient for whatever reason. Cheaper just to leave the sign up.