Oops, it doesn't look like 'monument the day' is a national day..

Other days

pumpkin

Pumpkin Day
bow tie

Bow Tie Day
artists

Artists Day
gum

Gum Day
martini

Martini Day
offer

Offer Day
kale

Kale Day
fiancee

Fiancee Day
tell a fairytale

Tell A Fairytale Day
stud

Stud Day