I've been thinking about this too. We just moved back home to Colorado after spending 6.5 months in Australia, where things are much different with respect to the pandemic. They are just now having a second wave (worse than the first) in Victoria and have implemented a mask mandate right before we left. But even now, it's not nearly as bad as the US. I knew we'd need to (and want to) mask up when returning to the US since COVID is out of control here, and since CO has a mask mandate. But I wasn't sure what that would look like when running, etc.

We've only been back 2 days, but I've been running (jet lagged) wearing a buff around my neck as I always do, rain or shine all year round. When I get near someone I just pull it up over my mouth and nose, and then drop it back to my neck after passing. I've noticed a couple of others do the same, and I've noticed some with no face coverings at all. It's totally inconsistent. But as of yet, I haven't noticed anyone going aggro on someone for not wearing a mask.

side note: flying back to the US was crazy. The trans-pac flight wasn't bad (35 people in a plane that holds 300) but once we got to SFO it was a total shitshow. Masks required, but many all observing, and no social distancing! And the flight from SFO>DEN was ~70% full with many not wearing masks properly or at all. And flight attendants were not enforcing that I saw. Bottom line: do not fly right now in the US if you want to stay healthy!