If they did declare a no-fly zone then they wouldn't be calling Putin's bluff, rather it would be NATO's bluff on whether or not they would enforce it which would be highly unlikely as it could be a catalyst for WW3.
Obviously this no-fly zone idea completely ignores the fact that NATO is a defensive organisation, so it's all a non-starter any way.
Maybe it is overt signalling to Russia, testing some of the prototype systems like ARTEMIS and/or ally interoperability in closer to real world situations but given the activity I've seen on Flight Radar over the last few days I'm not so sure they won't be pulling the bluff if this goes on much longer. It is almost unthinkable but the feeling I get from what I'm observing in terms of specific utilisation of assets and what, general patterns of missions, etc. doesn't fit with sitting back in a defensive posture and/or feeding Ukraine info forever.
EDIT: On a related note - whelp those F-15s are loud - just had some fly nearish my house but not that near and very audible.