Yes they are various places I have marked and saved as a “favorite” in the past when I was using Maps in iOS 9.x.
Finding these Place Marks in Maps (iOS 9.x) was a pain because you had to start a search to see the list. But at least they were only visible when I selected them. And they could be turned on individually. In Maps (iOS 10.x) it is the opposite — AFAIK all “favorites” are now always ON. They only show up if the map is zoomed into the area around them. But as you zoom in this can lead to clutter when you are looking to see the street names etc. in an area that has several “favorites” and lots of paid locations popping up. Both of these types of pop ups are bolder and much easier to read than the underlying street names.
This would be OK if my place marks were really “favorites” i.e. places I always want to see on the map anytime it is zoomed into that area. But often my place marks are simply the location of something that I would like to see on a map once in awhile e.g. only when I’m trying to remember the exact location of that specific item. So I really don’t want to see most of them them every time I investigate, walk/ride/drive by that location. A simple favorites toggle would do the trick.
Tap on the marker, pull up the info window, tap remove favorite. This doesn't get rid of the pin, so you can tap on the marker again, pull up the info window, and tap remove marker