Historical clue formulations

• Marks in the sand, perhaps — 2022-11-03
• Things picked up on beaches — 2020-02-15
• They usually come with bikinis — 2019-10-25
• Marks left by swimsuits — 2019-10-21
• Wristwatches may make them — 2016-04-02
• Bikini wearers' markings — 2007-10-29
• Results of sunbathing — 2003-09-21
• Borders on the beach? — 1998-10-03