As Anthony points out there is a minor difference between the graphical symbol in BS 5499 and ISO 7010 and are not likely to confuse anyone and I would totally agree that these signs do not require changing until they fall apart, however there are a huge number of escape route signs that are completely different in colour and design, specifically the so called Euro Sign but also derivitives of same with different reversed graphical symbol small arrows white blocks etc etc. Testing to ISO 9186 and Japanese consumer research has shown that these types of signs are not understood and have been clearly rejected. If the process of risk assessment is to work then this must be a significant finding.
The late Dr Jonathan Sime would always tell me that evacuees are all predesposed to react and try to leave buidings the way they came in and this may result in loss of ASET by time and elongated travel distance, he said his research pointed to the conclusion that in order to influence evacuee behaviour another way it would need to be of the highest integrity. This information would need to be continuous, unambiguous and the evacuee must be able to predict the next piece of information at any decision point if they are to remain confident and maintain effective egress. I have always adopted this as my guiding principle for safety wayguidance. The work of Tranter and Paul, most recently with Jake Paul as a function of stairway guidance in the aftermath of 9/11 has support this view.
There is plenty of evidence out there of evacuees being confused during evacuation, I have already mentioned Dusseldorf Airport and I recall the fatality of a middle aged couple in a hotel in Bolton on a Friday afternoon and in other statements of surviving evacuees recorded that there was confusion and not knowing where to go to escape. The fine to this hotel group was in six figures.
I agree with Anthony it is all a matter of priority, my advice is that the facts should be given to the Responsible Person and he will ultimately decide whether to take the risk. The facts are that so called Euro Signs are likely to confuse! The evidence is overwhelming!