Where are you from? Here's an example of a 1970s Coca-Cola bottle from Miami Florida. All of my American 60s and 70s Coca Cola bottles look the exact same on the bottom. I don't have any Canadian examples from that time period nor do I have any Coca-Cola bottles from around the 20s. In Canada Coca-Cola was bottled in clear bottles during the 1940s and the 1950s and they were probably made in clear bottles during those times in the United States as well. None of my 40s or 50s bottles have trademark bottle embossed on the bottom, but all of my 60s and 70s bottles do in the center. They also have a registered symbol. Because your bottle says trademark bottle on the bottom I'm leaning towards 60s or 70s rather than 20s but it's hard to say for sure without the top half. Hope this helps.