Planning permission is not normally required for a small sign, for instance with your house name or number on it.
Learn more about adverts and signs.
You may need to apply for advertisement consent to display an advertisement bigger than 0.3 square metres, however, and the planning regime for larger, professional adverts, signs for businesses etc. is complex.
Domestic adverts and signs are not normally subject to building control, although, if a lit sign, any electrical work would be. In all cases signs must 'be kept in a safe condition'.