Some days Webster is no help at all, eh Gene?

Crest: a heraldic device placed above the shield in a coat of arms, or used separately on seals, silverware, note paper, etc.

Seal: a design, initial, or other device placed on a letter, document, etc., as a mark of genuineness or authenticity.

Or you could assume it's a recommendation that your flipper-footed sea mammals practice good dental hygene.