On the inside you should have the standard fire exit sign based on graphic symbols, white on a green background, people should not need to be reminded to keep fire exits clear and unobstructed from the inside of the building because it should both be obvious and covered in basic fire safety awareness training.
But if this can be a problem at your premises a sign based on a Blue circle "Fire exit keep clear" can be provided inside as part of your risk control measures.
The outside face of a fire exit door should be provided with a sign based on a blue circle Fire exit keep clear if there is any possibility that persons, not aware that it is an exit, may obstruct the door in some way. Again the sign may be part of your risk control strategy- you may need to provide a bollard to stop people parking there for example.
Signs should conform to BS5499
