Historical clue formulations

• Lead-in to many a side thought, informally — 2025-04-03
• ), briefly — 2020-12-16
• Symbol over 9 or 0 on a keyboard, for short — 2018-03-04
• Emoticon element, for short — 2006-12-13
• Start of an aside, for short — 2003-05-25
• Figure above a 9 or 0, for short — 1998-06-27
• Punc. mark — 1997-03-15