What does the terms "Black Seal" mean on Panerai watches?

Panerai Radiomir PAM 183

The words "Black Seal" on the dial of Panerai watches refers to Italian Navy Special Operations divers who when donning their black wet suits looked like black seals.

Several Panerai watches have had the words "Black Seal" on their dial. These include the following models:

PAM00076 (Luminor 44 mm. Hours, minutes,seconds and date. Titanium)

PAM00183 (Radiomir 45mm. Hours, minutes and seconds)

PAM00287 (Radiomir 45mm. Hours, minutes,seconds and date)

PAM00292 (Radiomir 45mm. Hours, minutes and seconds. Ceramic)

PAM00380 (Radiomir 45mm. Hours, minutes and seconds)