Sterling silver does tarnish over time. The quickest fix is using a tarnish remover dip. Rinse in clean water and dry gently with a towel. Do not use a polishing cloth as that can remove the oxidation from the letters on the piece.
14kt gold vermeil can tarnish after long periods of exposure to sun and dust. When your piece tarnishes you may use a silver tarnish dip. Do not use a polishing cloth as that can remove trace amounts of gold from your piece.