"Warning - anybody except for aircrew must wear a hi-visibility jacket past this door".
Presumably they recognise that aircrew are aware that propellors bite.
The daft thing is that if you take the trouble to read the relevant CAP you will see that it is all about the danger of being run down by airside vehicles of the ground-based variety, which are generally very rare animals at most GA fields.
Aircraft are generally easily spotted by pedestrians as they are big, noisy, slow moving and have strobe lights and wings on them. People therefore tend not to get run over by them. Its the baggage tractor hurtling round the corner that's dangerous.
Mike