These appeared first on large vehicles - pickups and SUVs. They do have a large blind spot, so it was a logical addition. IIRC the first model year that these were available was 2002.
More vehicles have been adding these, and the forms vary. The original version (in Ford SUVs) was a red LED arrow on the end of the sideview mirror. These were an option, and not very many people opted for it. Now several companies are putting orange lights on the bottom/rear of the mirror. These are becoming standard equipment and more visible recently.
IMO these lights do more to prevent accidents than the mandatory high-mounted brake lights that were required from 1986 onward.