As shown in the figure:
Letter analysis
"D" may be the symbol of a door, just like ancient Egyptian hieroglyphics. We can't know when it first appeared in Sumerian characters.
About 1000 BC, this symbol was a specific linear form in Biblus (the ancient Mediterranean port city of Jubail, located in the north of Beirut, Lebanon, and became a prosperous Phoenician city in the second millennium), other parts of Phoenicia and the center of Canaan. In semitic, it is called th, which means door.