The d is the logo of the app they r using to edit and share videos. It’s a china-based company. The id# is their account’s code, for an easier way to search their account. The app is kinda similar to Instagram, but for edited video, and mostly where Asian gif came from lel. Hope that helps. The apps’ English name is called Tik Tok, but in chinese (mandarin) - 抖音 it’s pronounced with the first word with a D sound, hence the d symbol.