I've never heard of teller appreciation week. When I started in banking decades ago, we were supposed to refrain from showing excessive appreciation for the tellers.
Was that code for "Don't hug the tellers!"? Otherwise it just seems silly.
They* deserve appreciation 52 weeks out of the year, and anyone that's ever worked in that role understands it. (*Assuming that "they" are one of the ones that isn't the one twirling their gum and playing on their phone in between every transaction. But we have way more good ones than bad)