What’s the difference between grey and gray? It’s grAy in America, and grEy (almost) Everywhere else.
I’ve always found that interesting.
Anyway, another of those little bits is the Mr./Mr dichotomy. In the US we write a bit more formally than most of the rest of the English speakers of the world, so we add the period. Most other places don’t. I’ve usually stuck to that convention because it seems a bit jarring not to.
But no more. Today I throw off the chains of tradition, and live life to the fullest. I’m writing Mr/Mrs/Ms and living in infamy.
The most American English thing possible is adopting other bits of grammar because they’re useful. That is what we do. It’s our thing.