In the trading posts of the old west, the shopkeeper measured out a yard on his wooden counter and inserted twobrass thumbtacks. He used this to measure off "yard goods" such as fabrics and rope. So to set the price he first had to get down to brass tacks.
Marvyn: okay, well... if you wanna join me to watch some game film, you're welcome. TCKS
EMMA: stop saying that! No one says that, I don't even know what it means.
Marvyn: yeah, cause I just made it up.
Emma: what?
Marvyn: yeah, I made it up. TCKS. "take care. Keep safe."
Emma: but it no one but you know that, it's just a bunch of letters.