I think it's cool too and I'm not the kind of player who loves doing challenges etc but I did have fun searching around and looking for these. I also agree this system can be used in other ways making ways to get a small amount of ticks feeling a little bit more organic.
another positive thing about this is it brings in the community a little bit more. for example when I first stumbled onto one of these symbols I wasn't sure what it was for as another skater rolled up and did a trick on it so I gave him the question mark as he was leaving, he he came back and did the trick again and showed me what to do. Its little things like that I find enjoyable
another example, I joined a group with random players and we all went around the map searching together,, when someone found one he'd set a marker and we'd all spawn on his location, we spent a good 20 to 30 minutes doing that and it was just a different type of gameplay that felt refreshing and fun.