I am reading you have the common "Action in the event of fire" style notice which has been "stuck on the wall" without adding the necessary detail of where the assembly point is located (the blank space for writing or DYMO tape). For image example:

https://www.arco.co.uk/Web-Taxonomy/Signs/Fire-Safety-Signs/Fire-Action-Signs-and-Posters/PVC-%22Fire-Action-on-Discovering-Fire%22-Sign-200mm-x-300mm/p/PIMM00000000046619?sku=55TB405&queryId=043b93a3b1f12f3d899cdc1ef62a8c61

You dont need an external Fire Assembly Sign but what you do need is the internal instruction to say "at the front of the building" or "at the bottom of the car park" etc.

Hi MJ

Are these actions coming from some fire risk assessor who has failed to realise that fire legislation moved from "prescriptive" to "functional" over a decade ago?

....and thence thinks that one size fits all scenarios.

In my last place of work there were a few tenants spread over seven floors + a flat for the Building Manager and family above those.

Wouldn't be practical for all those working in the building to all assemble at the same place, nor even for our own 300 odd staff.

So, numerous assembly points (NONE immediately outside the building), on the opposite side of the streets each end of the building. 

Hence, what was important was that people on Floor X knew where THEIR assembly point would be. This done via information and training for staff + the induction video for visitors to our offices.

Any attempt to put all this down on Fire Evacation notices would have resulted in gross information overload.

If you are looking at relatively few people then perhaps an assembly point outside the building might work. But if that assembly point is M metres from the usual way in and out, why would you need to have it written down on a Fire Evacuation notice?

Perhaps your fire risk assessor might also like you to put up notices telling you which are the hot taps at each wash hand basin?!?! [I am assuming that your plumbing is to standard practice and that the taps are not the wrong way round!]