Signature is put on the front (artist name and surname) and on the back (all the relevant details: artwork name, artist name, materials, size, year and place).
Sides are coloured in continuous colours or colour of the artwork background.
Canvas is painted with background color even on the back side.
Artwork is covered with appropriate UV protective varnish (there is a time-lag to respect, oil should get dry through before applying a varnish).