[Crosseye_Jack]

YouTube already does, you have to "Tell YouTube" (Its basically a checkbox when you upload a video - https://i.imgur.com/mPZAKTX.png) if your content has paid promotion in it. https://support.google.com/youtube/answer/154235?hl=en

One of the reasons YT requires it is so they can replace an ad that conflicts with the contents paid promotion with something else (Another reason being FCC Regs).