Happy Mothers Day (brought to you by Hallmark)

Hallmark did not invent "Mother's day"!
I spuriously stated that this was a Made up holiday by Hallmark. I am wrong.

Modern antecedents and founding
One of the early calls to celebrate a Mother's Day in the United States was the "Mother's Day Proclamation" by Julia Ward Howe. Written in 1870, it was a pacifist reaction to the carnage of the American Civil War and the Franco-Prussian War. The Proclamation was tied to Howe's feminist belief that women had a responsibility to shape their societies at the political level.
In the years after the Mother's Day Proclamation, Ann Jarvis founded five Mothers' Day Work Clubs to improve sanitary and health conditions. In 1907, two years after Ann Jarvis' death, her daughter Anna Jarvis held a memorial for her mother and began a campaign to make "Mother's Day" a recognized holiday in the US. Although she was successful in 1914, she was already disappointed with its commericalization by the 1920s.
Spelling

In 1912, Anna Jarvis trademarked the phrases "second Sunday in May" and "Mother's Day", and created the Mother's Day International Association.
"She was specific about the location of the apostrophe; it was to be a singular possessive, for each family to honour their mother, not a plural possessive commemorating all mothers in the world."
This is also the spelling used by U.S. President Woodrow Wilson in the law making official the holiday in the U.S., by the U.S. Congress on bills, and by other U.S. presidents on their declarations.
Common usage in English language also dictates that the ostensibly singular possessive "Mother's Day" is the preferred spelling, although "Mothers' Day" (plural possessive) is not unheard of.

So There.  Sorry Mom.