Historical clue formulations

• Tipped off — 2023-01-14
• Made aware — 2022-07-01
• Let know — 2019-04-19
• Gave a heads-up — 2016-07-21
• Tipped off — 2012-09-30
• Given a tip — 2012-07-12
• Tipped off — 2011-03-11
• Tipped off — 2009-01-25
• On one's toes — 2004-01-22
• Warned — 1999-11-09
• Warned — 1999-10-04
• Sent smoke signals, maybe — 1998-11-22
• Tipped off — 1996-10-20
• Cautioned — 1995-06-18
• Put on guard — 1995-03-11
• Warned — 1994-03-28