Oops, it doesn't look like 'flag to mark day' is a national day..

Other days

polyamory

Polyamory Day
ruby

Ruby Day
book

Book Day
offer

Offer Day
bow tie

Bow Tie Day
pumpkin

Pumpkin Day
healing

Healing Day
latina equal pay

Latina Equal Pay Day
ask out your crush

Ask Out Your Crush Day
stud

Stud Day