Brief history on seals.
For centuries, letters have been closed, hot wax dripped onto the back of the envelope, and a seal pressed into the still warm was leaving an imprint of the seal. This would prevent anyone from opening the seal as once opened, this would break the wax seal.
Often the seals were engraved with an intaglio of a family crest or initials that would further prevent the letter being opened then re-sealed by someone else.
12ct gold antique seal from the 1870’s