Hello all, is exterior signage for fire exits a requirement, it makes sense regarding warning people not to block them with parked cars for example?

Broadly (as it can only be so as the legislation is functional, not specific and prescriptive) any final fire exit not in daily use as the main entrance that could be obstructed externally should be signed "Keep Clear - Fire Exit" using mandatory signage.

14.—(1) Where necessary in order to safeguard the safety of relevant persons, the responsible person must ensure that routes to emergency exits from premises and the exits themselves are kept clear at all times.

(2) The following requirements must be complied with in respect of premises where necessary (whether due to the features of the premises, the activity carried on there, any hazard present or any other relevant circumstances) in order to safeguard the safety of relevant persons—

(g)emergency routes and exits must be indicated by signs;